Judgment_paragraph 54 · Criminal proceedings against FU and Others (C-410/21)

54In the third place, it is necessary to bear in mind the importance attached, in the context of Regulations No 883/2004 and No 987/2009, to the principles of the application of the legislation of a single Member State, of sincere cooperation and of legal certainty, which underlie all the Court’s case-law on the binding effect of E 101 certificates. Whilst the principle of legal certainty is referred to in recital 6 of Regulation No 987/2009, the principle of the affiliation of employees to a single social security system is set out in recital 15 and Article 11(1) of Regulation No 883/2004, whereas the importance of the principle of sincere cooperation is clear from both Article 76 of Regulation No 883/2004 and recital 2 and Article 20 of Regulation No 987/2009 (see, to that effect, judgment of 6 September 2018, Alpenrind and Others, C‑527/16, EU:C:2018:669, paragraph 45).