In a statement the airline said that all its staff 'comply with EU laws by paying Irish tax and Irish social security arising from their work in Irish territory'.
The airline said it complies with all EU laws and regulations relating to transport employees, and that it is already taking an action in the European Court of Human Rights against France to challenge a 2007 decree covering similar accusations.
The threatened closure of its Marseille base has come about after an article in Le Figaro reported that the Aix-en-Provence Prosecutor’s Office accused Ryanair of operating 'clandestine work', 'illegal labour' and 'social dumping'.
Ryanair has said that if court proceedings are brought against it then four Irish registered aircraft will be transferred to other non-French bases in the EU, which will see a reduction in the number of Ryanair daily flights at Marseille from 33 to 16.
Ryanair’s Michael O’Leary said: "Should the Aix-en-Provence authorities initiate any Court action against Ryanair’s lawful Marseille operations, then jobs, traffic and inward investment will be lost in Marseille.
"The only people who benefit will be Air France, who will again have eliminated competition, while consumers and visitors at Marseille will suffer higher fares."