Ryanair is facing a €8.3m (£6.5m) penalty after losing an appeal against a decision that it broke French labour laws.
The AFP news agency said the no-frills carrier was found guilty of paying workers under Irish contracts to save money on payroll and other taxes.
The bulk of the money was in fines while €200,000 was for damages, the court ruled.
The ruling was issued a year after the original decision went against Ryanair.
At that time, the company said the majority of the financial penalties related to alleged non-payment of social insurance and state pension contributions in France for Ryanair crews.
The case centred around a facility operated by the company at Marignane, near the southern French cities of Marseille and Aix-en-Provence.
The company, run by its colourful chief executive Michael O'Leary, based four planes and 127 employees at the site without applying French labour law or filling out tax declarations in the country.
Ryanair argued that it did not have a permanent base in the area and that it was entitled to keep its workforce on Irish contracts, but prosecutors said its claim was not credible because the workers were living locally and the airline had offices there.
Ryanair was yet to provide a response to Sky News following the latest judgment.
Social charges in France are at around 40-45%, compared to 10.75% in Ireland.
The airline will have to pay damages to trade unions, France's social security system and pilots among others, AFP said.
