Judgment_paragraph 42 · 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)

42The opposite result would undermine the principle that employees are to be covered by only one social security system, would make it difficult to know which system is applicable and would consequently undermine legal certainty. In cases in which it was difficult to determine the system applicable, each of the competent institutions of the two Member States concerned would be inclined to take the view, to the detriment of the workers concerned, that its own social security system was applicable to those workers (judgment of 26 January 2006, Herbosch Kiere, C‑2/05, EU:C:2006:69, paragraph 25 and the case-law cited).