Judgment_paragraph 38 · A-Rosa Flussschiff GmbH v Union de recouvrement des cotisations de sécurité sociale et d’allocations familiales d’Alsace (Urssaf), venant aux droits de l’Urssaf du Bas-Rhin and Sozialversicherungsanstalt des Kantons Graubünden (C-620/15)

38On that certificate, the competent institution of the Member State in which an undertaking employing the workers concerned is established declares that its own social security system will remain applicable to those workers. By virtue of the principle that workers must be covered by only one social security system, the certificate thus necessarily implies that the other Member State’s social security system cannot apply (judgment of 26 January 2006, Herbosch Kiere, C‑2/05, EU:C:2006:69, paragraph 21 and the case-law cited).