Claire Hocquet, a lawyer for the SNPL pilots union that brought the case, said the court in Aix-en-Provence found the airline broke the law by not paying French social security and pension contributions for employees of its Marseille hub between 2006 and 2010. She said it also fined the Irish airline 200,000 euros ($270,440).
The court rejected Ryanair's argument that because its pilots worked in Irish-registered jets, it should be permitted to pay these charges in Ireland rather than France.
Ryanair has already said it will appeal the ruling. In a statement, the airline said French law and EU regulations are in contradiction on the question of where employment charges must be paid.
The case echoed a similar ruling in 2010 against rival low-cost airline easyJet PLC. The British company was convicted for keeping 170 workers at Orly airport south of Paris on British contracts between 2003 and 2006, and ordered to pay 1.55 million euros in damages and fines.