Alpenrind and Others

the Court (First Chamber) ruled:

1.      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.

2.      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State in which the activity is carried out and the courts of that Member State so long as the certificate has not been withdrawn or declared invalid by the Member State in which was issued, even though the competent authorities of the latter Member State and the Member State in which the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for the Coordination of Social Security Systems which held that that certificate was incorrectly issued and should be withdrawn.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.

3.      Article 12(1) of Regulation No 883/2004, as amended by Regulation No 1244/2010, must be interpreted as meaning that, if a worker who is posted by his employer to carry out work in another Member State is replaced by another worker posted by another employer, the latter employee must be regarded as being ‘sent to replace another person’, within the meaning of that provision, so that he cannot benefit from the special rules laid down in that provision in order to remain subject to the legislation of the Member State in which his employer normally carries out its activities.

The fact that the employers of the two workers concerned have their registered offices in the same Member State or that they may have personal or organisational links is irrelevant in that respect.