Not every organisational change constitutes a substantial modification. However, when a measure materially alters working hours, schedules, shift arrangements, remuneration systems, salary levels, working methods, performance standards or job functions, the company must carefully consider whether it needs to follow the procedure set out in Article 41 of the Workers' Statute.
Misclassifying such a measure can have serious consequences: legal challenge, a judicial declaration that the measure is unjustified or void, reinstatement of the employee to their previous conditions, liability for damages, collective dispute, or even a compensated termination of contract if the conditions of Article 50 of the Workers' Statute are met.
This article covers the full legal framework of Article 41 of the Workers' Statute: what qualifies as a substantial modification, which procedure the company must follow, what deadlines apply, what options the employee has, and what consequences may flow from the ruling. If your situation specifically involves the loss of commissions, changes to a client portfolio, or a reduction in variable salary, we also recommend reading the dedicated guide on substantial modification and variable salary, which covers in depth the burofax strategy, the twenty-day time limit, and a real case discussed on video by the Conesa Legal employment law team.
Written by:
Zaida Álvarez
Employment Lawyer
Josep Conesa
employment lawyer
What constitutes a substantial modification of working conditions under Article 41 of the Workers' Statute
A substantial modification of working conditions is a management decision that materially alters employment conditions in a way that has a real impact on the employee's work performance or their economic or professional position. The primary legal framework is set out in Article 41 of the Workers' Statute.
Article 41 of the Workers' Statute allows the company to implement substantial modifications where there are demonstrable economic, technical, organisational or production-related reasons. The legislation expressly identifies the following as matters that may constitute a substantial modification:
- working hours;
- schedule and distribution of working time;
- shift work arrangements;
- remuneration system and salary amount;
- work system and performance targets;
- job functions, where they exceed the limits of functional mobility.
A reduction in variable salary, a significant change to working hours, a shift pattern change, a modification to the commission structure, or a functional reassignment that effectively empties the role of its content may not be simple internal organisational decisions. They may require a formal procedure to be followed as a substantial modification of working conditions.
Which workplace changes may qualify as a substantial modification: working hours, salary, schedule and job functions
Whether a modification is deemed substantial depends not only on the subject matter affected, but also on the degree of change involved. The company has scope to direct and organise its workforce, but that scope does not extend to materially altering essential employment conditions without following the appropriate procedure.
The following changes, among others, may give rise to a substantial modification:
- a significant reduction or alteration of variable salary;
- a change to the commission structure or performance targets;
- a substantial change to working hours or the distribution of working time;
- an alteration to the shift work arrangement;
- a significant change to overall working hours;
- a change to the work system or performance targets;
- functional reassignment that goes beyond ordinary functional mobility;
- transfer to residual or substantively empty roles;
- organisational changes that affect the ability to generate bonuses or variable pay.
The key is not how the company labels the measure. What matters is its actual effect. If the change materially affects salary, duties, working hours, schedule, performance or professional standing, it must be assessed as a potential substantial modification.
What procedure must the company follow to modify working conditions
The first mistake to avoid is using the wrong legal route. There is an important distinction between a negotiated change, ordinary functional mobility, an individual substantial modification, a collective substantial modification, and the non-application of a collective bargaining agreement. The correct route depends on the origin of the condition being affected and the number of employees involved.
Individual substantial modification: written notice and a 15-day notice period
If the change affects an individual condition or one enjoyed by the employee personally, and does not exceed the collective thresholds, it may qualify as an individual substantial modification.
The company must notify the affected employee and their legal representatives in writing at least fifteen days before the measure takes effect. The notice cannot be limited to a generic instruction. It must identify the measure, explain the reasons behind it, specify the effective date, and allow the employee to understand clearly what is changing and why.
Collective substantial modification: thresholds, consultation period and agreement
If the measure affects a significant number of employees within a ninety-day period, it constitutes a collective substantial modification.
Under Spanish law, a modification is considered collective when it affects, within ninety days, at least:
- 10 employees in companies with fewer than 100 workers;
- 10% of the workforce in companies with between 100 and 300 workers;
- 30 employees in companies with more than 300 workers.
In these cases, the company must open a consultation period with the employees' legal representatives. This cannot be a hollow formality. It must focus on the reasons for the measure, the possibility of avoiding or reducing its effects, and the steps needed to mitigate its consequences.
If the procedure ends in agreement, the existence of grounds is presumed, although the agreement may be challenged in cases of fraud, deceit, coercion or abuse of rights. For a deeper analysis of the applicable judicial review standards, please refer to the commentary on case law concerning collective modification of working conditions.
Substantial modification or collective agreement opt-out: when to apply Article 82.3 of the Workers' Statute
If the condition to be modified is set out in a statutory collective bargaining agreement, the applicable route may not be Article 41 of the Workers' Statute but rather Article 82.3 of the Workers' Statute, which governs the non-application of collective agreements, also known as an opt-out (descuelgue), subject to one important limitation: any such opt-out is always temporary, never permanent.
This distinction is critical. A company cannot modify, via Article 41 of the Workers' Statute, a condition established in a statutory collective bargaining agreement. For this reason, before taking any action, it is advisable to develop a sound employment strategy and identify the origin of the condition in question: whether it derives from an individual contract, a collective agreement, a unilateral employer decision with collective effect, a statutory collective bargaining agreement, or an established custom and practice. The appropriate legal route depends entirely on a correct initial assessment, and will shape all subsequent collective bargaining over working conditions.
Remote working and substantial modification: the limits of Article 41 of the Workers' Statute
Certain matters are also governed by their own specific legislation, such as the remote working contract. A relevant example is distance working. Law 10/2021 establishes that distance working is voluntary and that any modification to a distance working agreement must be formalised in writing. Article 41 of the Workers' Statute should not be used as an automatic mechanism to impose changes in an area subject to specific regulation. In many cases, poorly drafted agreements can give rise to substantial modifications of working conditions, including collective ones, for example, when no distinction is drawn between a distance working contract and a remote working contract (teletrabajo), as if the two were identical.
Accordingly, the limits of Article 41 of the Workers' Statute are particularly relevant to decisions concerning remote working, on-site attendance percentages, place of work, reversibility arrangements, and the objective grounds required where a company refuses an employee's request to reconcile family and professional life through remote working. It is strongly advisable for the company to first review the individual agreement, internal policy, the applicable collective bargaining agreement and specific legislation, and to seek the precise advice of a employment lawyer.
How to implement a substantial modification of working conditions while minimising legal risk
For a substantial modification to have any real prospect of surviving a legal challenge, it is not enough for the company to have an organisational need. It must be able to explain that need, document it, and follow the correct procedure. The preparatory stage is critical: a well-constructed measure can withstand litigation; one applied without a proper paper trail rarely does.
In the case of an individual substantial modification, the company must prepare a clear written communication identifying the measure, its effective date, the reasons justifying it, and its impact on the employee concerned. A verbal instruction, an informal email, or an ambiguous notice is not sufficient.
In the case of a collective substantial modification, the company must open the corresponding consultation period. During that period, the parties must examine the grounds for the measure, the possibility of avoiding or mitigating its effects, and any available alternatives.
As a minimum, the company should document four elements:
- the specific ground justifying the measure (economic, technical, organisational, or production-related);
- the actual impact of the change on the workforce or on the individual affected;
- the less harmful alternatives that were considered;
- a clear record of the negotiation carried out or the communication provided.
Many disputes arise not from the measure itself, but from the absence of a robust justification. If the company cannot demonstrate that the change was necessary, proportionate, and properly communicated, the litigation risk increases significantly.
That risk is even greater when the measure affects variable salary, commissions, older employees, individuals with enhanced legal protection, employees on sick leave, those exercising work-life balance rights, maternity or paternity rights, or any other matter that may engage fundamental rights or give rise to a discrimination claim.
Variable salary and commissions: when to consult a dedicated guide
One of the most contentious areas is the modification of variable salary. Many companies do not directly reduce the fixed salary, but instead change an employee's duties, area of activity, targets, or assigned portfolio. The result may be a significant indirect loss of commissions or incentives, even where the fixed element of the payslip remains unchanged.
In such cases, the measure may affect the remuneration structure and the employee's realistic income expectations, which can be regarded as a substantial modification of working conditions. When a company reassigns a sales employee, changes their territory, removes their client portfolio, transforms their targets, or moves them to a role with no real capacity to generate variable pay, it must assess whether a substantial modification has occurred, and anticipate the consequences that such a change may entail.
The fact that the financial loss is projected into the future does not eliminate the risk. If the change makes a significant reduction in variable pay foreseeable, it is worth considering whether the measure affects the remuneration structure and the overall level of pay.
Variable salary raises its own procedural complexities, the twenty-day time limit, the paradox of future loss, the strategy of serving formal notice by burofax, and the conflicting positions of different High Courts of Justice. For that reason, we have dedicated a specific guide to this topic: substantial modification and variable salary: when to challenge the loss of commissions.
Functional reassignment or substantial modification: key distinctions for the company and the employee
Not every change in duties amounts to a substantial modification. The company has a degree of latitude to reassign employees within their professional group (also referred to as horizontal mobility), provided it respects the employee's dignity, training, professional grade, and the applicable legal limits.
The issue arises when a change in duties materially alters the content of the role, strips the employee of responsibility, separates them from their team without adequate explanation, assigns them to residual tasks, or directly affects their remuneration structure.
In such cases, the company may argue that the change constitutes horizontal mobility or an ordinary reorganisation. However, if the change has a significant impact on duties, salary, variable pay, career progression, or dignity, a compelling case can be made that it in fact constitutes a substantial modification.
The dividing line is not always clear. For that reason, before communicating the measure, it is advisable to assess not only the employee's employee formal job title, but the actual content of their role both before and after the change. The same decision may appear neutral on an organisational chart, yet be substantial in terms of the day-to-day reality of the position.
What options does the employee have when faced with a substantial change to working conditions
The employee may accept the measure, challenge it, terminate the contract under Article 41.3 of the Workers' Statute, or pursue an indemnified termination under Article 50 of the Workers' Statute combined with protection of fundamental rights. The right course of action depends on the specific circumstances, the procedure followed by the company, and the actual impact on the employment relationship.
The employee may accept the measure and continue working under the new conditions.
The employee may challenge the employer's decision before the employment courts if they consider it to be unjustified, procedurally flawed, or in breach of their rights.
In certain circumstances, if the change is detrimental to the employee, they may request termination of the contract with compensation of twenty days' salary per year of service, up to a maximum of nine monthly payments. This option is provided for under Article 41.3 of the Workers' Statute.
Furthermore, if the change is made without following the legally required procedure and affects the employee's dignity, the route provided under Article 50.1.a of the Workers' Statute may become available, allowing the employee to seek indemnified termination where substantial changes have been made in breach of Article 41 of the Workers' Statute and to the detriment of their dignity. Article 50.1.c of the Workers' Statute opens the same route in cases of any other serious breach by the employer. In both cases, the compensation may be equivalent to that awarded for unfair dismissal.
For the company, this means that a poorly handled change to working conditions may not only result in the reinstatement of the original terms. It can also lead to an indemnified termination, a claim for damages, or a dispute over the violation of fundamental rights.
Time limit for challenging a substantial change: 20 working days from notification
The general time limit for challenging a substantial change to working conditions is twenty working days from written notification of the employer's decision. This is a strict expiry deadline, not a limitation period.
This deadline is one of the most sensitive points in practice. For the company, a defective notification may give rise to disputes about when the clock started running. For the employee, allowing the deadline to pass may foreclose any avenue for challenge. It is a particularly delicate issue because the Supreme Court has established that, if the employee is already aware of the measure because it is being applied, formal written notification by the company is not required for time to begin running, in other words, if the employee acquiesces to the change, they cannot subsequently claim that their working conditions were unilaterally altered. This matters because twenty working days pass very quickly, and changes to working conditions are often neither immediately obvious nor of instant effect. This means that the employee would be well advised to seek the guidance of an experienced employment lawyer to identify alternative avenues for contesting, rather than accepting, a substantial change to working conditions implemented by the company without complying with the formalities required by law. If you are in this situation, please get in touch: we know how to find solutions:
This is why, when a change is communicated verbally, as an informal instruction, or is applied without a formal written notice, the procedural dispute becomes considerably more complex. The practical recommendation in these cases is to respond by burofax (a certified postal service with legal evidentiary value) within the first few days, in order to establish your position on record and preserve the relevant deadlines. This point and the procedural strategy around burofax are covered in detail in the guide on substantial modification and variable salary.
From a business perspective, the recommendation is clear: if a measure is significant, it must be communicated in writing, in full, and in a traceable manner. Not merely for the sake of formal compliance, but because clear written communication structures the dispute, fixes the start of applicable deadlines, and provides a stronger basis for defending the decision.
When a substantial modification may be unjustified or void
The ruling resolving a challenge to a substantial modification may declare the measure justified, unjustified, or void. Each classification carries different consequences.
The measure will be deemed justified where the company can demonstrate the grounds invoked and the correct procedure has been followed.
It will be deemed unjustified where the company fails to prove the stated grounds, or where the measure is found to be unreasonable or disproportionate. In that case, the employee will be entitled to reinstatement of their previous working conditions and to claim damages for the period during which the measure was in effect.
The measure may be declared void where it is adopted in abuse of law, where the consultation period is bypassed in a collective modification, or where it infringes fundamental rights. Nullity may also arise where the measure conceals discrimination on grounds of age, sex, disability, origin, health, work-life balance, or any other protected characteristic. Law 15/2022, the comprehensive equality of treatment and non-discrimination act, strengthens the anti-discrimination framework applicable in the employment context.
In such cases, the company faces not only annulment of the measure, but also potential additional compensation for non-material damages or infringement of fundamental rights.
Where the employee provides reasonable evidence of discrimination or infringement of fundamental rights, the company must demonstrate an objective, reasonable, and proportionate justification for its decision. Prior documentation and the overall consistency of the measure are critical at this stage.
Common mistakes companies make when implementing a substantial modification
Substantial modification is a useful tool, but it is also one of the business decisions most likely to generate conflict when applied hastily. Common mistakes include:
- treating a substantial measure as though it were a simple internal instruction;
- communicating the change verbally or via an ambiguous email;
- failing to properly identify the economic, technical, organisational or production-related grounds;
- failing to quantify the real impact of the measure;
- not considering less disruptive alternatives;
- applying Article 41 of the Workers' Statute when the condition derives from a collective agreement and may instead require Article 82.3;
- modifying the variable salary without analysing its actual weight in the overall remuneration package;
- confusing functional mobility with effectively hollowing out a role;
- implementing successive changes to avoid triggering the thresholds for a collective modification;
- affecting employees approaching retirement, on sick leave, or under special protection without a reinforced justification;
- failing to document the negotiation process or the consultation period;
- not anticipating the risk of collective disputes or an accumulation of individual legal challenges.
Most of these mistakes share a common thread: the company acts before building the supporting case file. In a substantial modification, moving quickly does not always mean moving wisely.
Legal checklist before notifying a substantial modification
Before communicating any modification, it is advisable to review the following elements:
- Does the measure affect fixed or variable salary? It may trigger Article 41 of the Workers' Statute by affecting the remuneration structure or salary amount.
- Are working hours, schedules or shift patterns being changed? These are matters expressly covered by Article 41 of the Workers' Statute.
- Does the condition derive from an individual contract, a collective agreement, or a statutory collective agreement? The applicable legal route may differ. If it derives from a statutory collective agreement, it may be necessary to proceed under Article 82.3 of the Workers' Statute.
- Does the measure affect several employees within a 90-day period? It may constitute a collective modification and require a formal consultation period.
- Are there particularly vulnerable individuals involved, or any indications of discrimination? There may be a risk of the modification being declared null and void, as well as liability for infringement of fundamental rights.
- Is there a clear and complete written communication? The absence of a formal letter can create problems with evidence, deadlines, and justification.
- Has the company documented the grounds? Without demonstrable grounds, the measure may be declared unjustified.
- Have less detrimental alternatives been considered? This strengthens the proportionality of the measure.
- Does the measure affect commissions, targets, or client portfolios? There may be a financial impact even if the fixed salary does not change.
- Has a negotiation strategy been prepared? This is essential when the measure is collective in nature or likely to give rise to a dispute.
When the objective is to reorganise without damaging the employment relationship, the most prudent course is not to implement the measure hastily, but to plan the approach carefully, document the grounds, negotiate where appropriate, and communicate with precision.
Frequently asked questions on Article 41 of the Workers' Statute and substantial modification of working conditions
What is a substantial modification of working conditions?
It is a management decision that materially alters essential terms of the employment relationship, such as working hours, timetable, shifts, remuneration structure, salary amount, work organisation, performance standards, or job functions. The primary legal framework is Article 41 of the Workers' Statute.
Can the company change an employee's working hours through a substantial modification?
Yes, provided there are economic, technical, organisational, or production-related grounds and the relevant legal procedure is followed. If the change is material and affects working hours or the distribution of working time, it falls within the scope of Article 41 of the Workers' Statute.
Can the company reduce variable salary?
This depends on how the variable component is structured and the extent of the change. If the company modifies targets, functions, client portfolios, market scope, or the commission structure in a way that materially affects total remuneration, this may constitute a substantial modification, even if the fixed element of the payslip remains unchanged. This issue is examined in detail in the guide on substantial modification and variable salary.
What is the deadline for the employee to challenge the decision?
The general deadline is twenty working days from the date of written notification of the employer's decision. This is a strict limitation period, it cannot be extended. For this reason, it is important to act promptly when faced with any material change, to record any objection in writing, and to consult your trusted employment lawyer to assess whether, on formal grounds, a challenge may be possible within the ordinary one-year limitation period.
What happens if the company fails to notify the change in writing?
If this occurs, please contact us. Failure to provide written notification is poor practice and can create significant problems for the company: disputes over when the time limit begins to run, difficulties in proving the measure was implemented, challenges in justifying the grounds, and questions about whether the correct procedure was followed. In practice, when no written notice is provided, the employee typically responds by sending a recorded delivery letter (burofax) to establish their position and protect the twenty-day deadline, or we can explore other avenues for challenge that are not subject to the 20-day limitation period.
Can the employee terminate their contract if they do not accept the change?
In certain circumstances, yes. If the change is detrimental and affects the matters specified by law, the employee may request termination of their contract with compensation of twenty days' pay per year of service, up to a maximum of nine months' salary (Article 41.3 of the Workers' Statute). Where there is also a serious breach by the employer and an infringement of the employee's dignity, a claim may be brought under Articles 50.1.a and 50.1.c of the Workers' Statute, entitling the employee to compensation equivalent to that awarded for unfair dismissal.
When does a substantial change qualify as collective?
When, within a ninety-day period, it affects at least 10 employees in companies with fewer than 100 workers, at least 10% of the workforce in companies with between 100 and 300 employees, or at least 30 employees in companies with more than 300 workers.
What is the difference between a substantial change and opting out of a collective agreement?
Article 41 of the Workers' Statute allows employers to modify certain working conditions. However, where a condition is set out in a statutory collective bargaining agreement, the company may need to rely on Article 82.3 of the Workers' Statute, which governs the non-application (or 'opt-out') of collective agreements. Choosing the wrong legal route can jeopardise the entire measure.
Can a substantial change be declared null and void?
Yes. A change may be declared null and void if it is made in abuse of law, if the mandatory consultation period is circumvented in the case of a collective change, or if it infringes fundamental rights, for example, if it conceals discrimination on grounds of age, sex, disability, health, work-life balance or any other protected characteristic. Law 15/2022 strengthens the anti-discrimination framework applicable in the employment context.
Can age discrimination occur in an internal reorganisation?
Yes. An internal reorganisation that appears neutral on its face may be discriminatory if it disproportionately affects an individual employee on account of their age or proximity to retirement, particularly where the company cannot demonstrate an objective, reasonable and proportionate justification for applying the measure to that specific person.
Is a pre-trial conciliation request required before filing a claim?
Proceedings for substantial modification of working conditions follow an expedited process and do not require prior conciliation in the same way as other employment proceedings. Even so, it is advisable to analyse each case individually before taking action.
Can the company impose a return to remote working under Article 41 of the Workers' Statute?
This should not be treated as an automatic mechanism. Remote working is governed by specific legislation and is based on the principles of voluntariness and written agreement. If the company wishes to modify remote working conditions, on-site attendance requirements, or reversibility arrangements, it must review the remote working agreement, internal policy, the applicable collective bargaining agreement, and Law 10/2021.
Employment lawyers for implementing or challenging a substantial modification
A poorly handled substantial modification may seem like a quick fix, but it can quickly become a far greater problem. It is essential to get both the process and the substance right, anticipating individual challenges, collective disputes, nullity, moral damages, loss of internal trust, or deadlock with employee representatives.
At Conesa Legal, we advise employers on the analysis, design, and implementation of substantial modifications to working conditions, and employees on challenging measures that affect their terms of employment. Our employment team can assess the appropriate legal route, prepare the necessary documentation, support the consultation period, evaluate the risk of nullity or discrimination, and develop a litigation strategy if the matter reaches a tribunal.
When the company needs to reorganise working conditions, the critical moment is not the hearing. It is the preliminary phase: correctly classifying the measure, documenting the grounds, communicating with precision, and anticipating risks before acting.
Contact our employment team to review your situation:
