Article 5(1) of Regulation (EC) No 987/2009 of the European Parliament and of the Council of 16 September 2009 laying down the procedure for implementing Regulation (EC) No 883/2004, as amended by Commission Regulation (EU) No 1244/2010 of 9 December 2010, read together with Article 19(2) of Regulation No 987/2009, as amended by Regulation No 1244/2010, must be interpreted as meaning that an A1 certificate, issued by the competent institution of a Member State under Article 12(1) of Regulation (EC) No 883/2004 of the European Parliament and of the Council of 29 April 2004 on the coordination of social security systems, as amended by Regulation No 1244/2010, binds not only the institutions of the Member State in which the activity is carried out, but also the courts of that Member State.

Article 5(1) of Regulation No 987/2009, as amended by Regulation No 1244/2010, read together with Article 19(2) of Regulation No 987/2009, as amended by Regulation No 1244/2010, must be interpreted as meaning that an A1 certificate issued by the competent institution of a Member State under Article 12(1) of Regulation No 883/2004, as amended by Regulation No 1244/2010, is binding on both the social security institutions of the Member State in which the activity is carried out and the courts of that Member State so long as the certificate has not been withdrawn or declared invalid by the Member State in which was issued, even though the competent authorities of the latter Member State and the Member State in which the activity is carried out have brought the matter before the Administrative Commission for the Coordination of Social Security Systems which held that that certificate was incorrectly issued and should be withdrawn.

Article 5(1) of Regulation No 987/2009, as amended by Regulation No 1244/2010, read together with Article 19(2) thereof, as amended by Regulation No 1244/2010, must be interpreted as meaning that an A1 certificate issued by the competent institution of a Member State under Article 12(1) of Regulation No 883/2004, as amended by Regulation No 1244/2010, binds both social security institutions of the Member State in which the activity is carried out and the courts of that Member State, if appropriate with retroactive effect, even though that certificate was issued only after that Member State determined that the worker concerned was subject to compulsory insurance under its legislation.

Therefore, it must be held that the Administrative Commission’s role in the procedure laid down in Article 5(2) to (4) of Regulation No 987/2009 is merely to reconcile the points of view of the competent authorities of the Member State which brought the matter before it.

That finding is not called into question by Article 89(3) of Regulation No 987/2009, which provides that the competent authorities must ensure that their institutions are aware of and apply all the EU provisions, legislative or otherwise, including the decisions of the Administrative Commission, in the areas covered by Regulations Nos 883/2004 and 987/2009 and under the conditions for which they provide, since that provision does not intend in any way to change the role of the Administrative Commission within the framework of the procedure to which it refers in the preceding paragraph and thus the status of an opinion on the conclusions reached by that commission in that procedure

(see paras 62-64, 77, operative part 2)