The A1 document is a European certificate issued by the country of origin of posted workers. This document indicates the legislation applicable to the posted worker. This document is one of the ways of ensuring that the posted worker's social security contributions are correctly paid from the country of origin. It is therefore useful, for example, for posted workers who work in several EU countries and wish to keep track of the payment of social security contributions in countries other than their country of origin. It also proves that the company hiring the temporary workers is tax compliant in the country of origin, and has no debts to the local tax authorities.
Yes, the A1 certificate is compulsory for any assignment lasting less than 24 months (the maximum duration of a posting). This means that even if you employ posted workers for a very short assignment lasting only a few hours or days, the A1 document will still be required.
The A1 document is issued by the seconded employee's health insurance fund. Filing an application for a certificate and issuing the A1 document is the responsibility of the seconded worker's company and not that of the customer.
Examples of professions that regularly use secondment: