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These notices of newly hired employees/workers, terminated employees/workers, and changes in employee or worker salaries or wages are filed with the Instituto Mexicano del Seguro Social (Mexican Social Security Institute) known as IMSS.

Companies are required by law to register or enroll newly hired employees/workers with the IMSS, or give notice of employees who leave the company, or are layed off or fired by the company, as well as to give notice or update the IMSS as to whether an employee or worker's salary or wage is changed (usually an increase)

The employer pays a portion of social security taxes and the other portion is withheld from the employee or worker's salary or wages and then paid to the IMSS authorities.

The IMSS also conducts field audits of entities that fail to submit these notices and keep the IMSS up to date with their information. If a company is audited by the IMSS for social security tax purposes, IMSS personnel come in like gangbusters. It is worse than being audited by the SHCP (Hacienda).
Hope this helps

Reference: Tom West's Dictionary

More than 18 years experience translating for the Mexico City financial community.

No points! Just paraphrasing Richard's answer.

I suppose one could come up with different names, it's a specific IMSS term.