The budget airlines were appealing against laws introduced last year which compels foreign airlines to apply French employment laws for crews of aircraft based at the country’s airports.
Ryanair, based in Ireland, argued that the rule breached European laws on the free movement of workers.
But the Conseil d’Etat dismissed the claim and ordered both airlines to pay 2,500 euros (£1,700) in legal costs.
Richard Martin, employment partner at law firm Speechly Bircham, said: “This will be seen as French protectionism towards its employee-friendly labour laws, but in reality a similar view would be taken by English courts and tribunals with regard to our own employment protection legislation to flight crews operating out of the UK.”
Ryanair said it would appeal the decision.