Although member states can disregard certificates which are obtained or relied on fraudulently, they must first implement the European procedure for dialogue between the institutions provided for this purpose.

In the judgment of principle in joined cases C-370/17 and C-37/18 Vueling, the ECJ has reminded the French courts of the primacy of European law over national provisions on the posting of workers.

As part of an investigation carried out at Paris Charles de Gaulle Airport and going back to 2007/2008, the French Labour Inspectorate had drawn up a report of concealed work against airline Vueling on the grounds that flight crews based at that airport were affiliated to Spanish social security rather than to French social security.

Vueling availed itself of A1 (ex-E101) certificates issued by the Spanish social security body, authorising the continued affiliation of its flying personnel to Spanish social security throughout the period of posting, in accordance with EU internal market rules.

The airline was nevertheless prosecuted before French courts and was convicted for concealed work by the Paris Court of Appeal in January 2012, confirmed by the Criminal Division of the Court of Cassation in March 2014.

In its ruling on Thursday, the ECJ stated that the French judge cannot unilaterally rely on alleged fraud to set aside certificates validly issued by the authorities of another member state without first having implemented the European procedure for dialogue between the institutions provided for this purpose.

In the case of Vueling, the ECJ found that the French courts disregarded this procedure, since they rejected the posting certificates held by the company’s flight crews prior to the French social security agency referring the matter to the Spanish competent body having issued the said certificates.

The Grand Chamber judgment also rules on another major principle of EU law: the principle of the primacy of EU law precludes a court of a member state from convicting a civil litigant in application of the res judicata effect of criminal judgments over civil proceedings (as is the case in France), where the criminal conviction at issue is based on a definitive finding of fraud made in breach of EU law.

Vueling was advised by a multi-disciplinary team at the Paris and Brussels offices of international law firm Gide, including partners Benoit Le Bret and Foulques de Rostolan, senior counsel Francis Kessler, counsel Yan-Eric Logeais and senior associate Diana Calciu.