Judgment_paragraph 56 · Criminal proceedings against FU and Others (C-410/21)

56Moreover, in such a situation, the lack of binding effects of the A1 certificate at issue would allow the institutions of the other Member States, and in particular the institutions of the Member State which had expressed doubts as to the accuracy and validity of that certificate, to make the worker concerned subject to their own social security system. Thus, an interpretation of Article 5 of Regulation No 987/2009 allowing the issuing institution provisionally to suspend an A1 certificate, by removing its binding effects for that provisional period, would be likely to increase the risk of duplication of social security systems, which would undermine the principle that employed persons are affiliated to a single social security system and the foreseeability of which system is applicable and, therefore, the principle of legal certainty (see to that effect, as regards Regulation No 1408/71, judgment of 2 April 2020, CRPNPAC and Vueling Airlines, C‑370/17 and C‑37/18, EU:C:2020:260, paragraph 70 and the case-law cited).