Press Release: Judgment in Case C-527/16. Alpenrind and Others

A posted worker is covered by the social security system of his place of work if he replaces another posted worker, even if those workers were not posted by the same employer.

However, an A1 certificate showing the affiliation of the worker to the social security system of the Member State of origin is binding, both on the social security institutions and the court of the Member State in which the work is carried out, except in cases of fraud or abuse, so long as it has not been withdrawn or declared invalid by the Member State of origin.