Failure to provide the employee with the social security contributions certificate for the last 180 days (or to submit it to the Public Employment Service (SEPE)) may constitute a serious infringement:
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Article 22.6 LISOS: "Failure to deliver to the employee, in due time and form, all documents required for the application and processing of any benefits, including the company certificate, or failure to transmit said certificate, in the case of parties required or opted into submission via electronic, IT or telematic means, in accordance with the established procedure."
And the Labour Inspectorate never misses a trick...

The fine can range from €750 to €7,500...
"Article 40. Amount of penalties.
1. Infringements in the field of employment relations and employment, in the field of Social Security, without prejudice to the provisions of paragraph 3 below, in the field of migration and employment of foreign nationals, in the field of temporary employment agencies and user companies, except those relating to occupational health and safety matters, which shall fall under paragraph 2 of this article, as well as infringements involving obstruction, shall be penalised as follows:
b) Serious infringements with a fine, at its minimum level, of €751 to €1,500; at its intermediate level of €1,501 to €3,750; and at its maximum level of €3,751 to €7,500."
In practice, however, the penalty is typically set at the lower end, at €751. Here is a real example:

And then comes the final twist before the penalty is imposed: pay promptly and we will reduce the fine. Although the Constitutional Court has declared this practice lawful (as with traffic fines, for example), in our humble opinion it suggests that either the €751 fine is considered excessive, or there is poor administrative management that has left the courts overwhelmed due to lack of resources, so the authorities are simply trying to collect less through this "offer":

In the end, with early payment, the penalty can/typically amounts to €450.60.