Posted work: On Tuesday 6 February, the Court of Justice of the European Union (CJEU) considered that the certificate fraudulently delivered to a posted worker could be "rejected" by a jurisdiction of the country hosting the same employee.
An employee sent for a mission abroad is granted a certificate of posting by the country where his company is located; this form (A1) proves that he is affiliated to the Social Security of his State of origin and that it is to him that he will pay his contributions, not to that of the host country.
However, many abuses have been observed ...
more info: http://www.lemonde.fr/economie/article/2018/02/07/travail-detache-la-cour-de-luxembourg-feature-a-dogme_5253035_3234.html