The European Commission has said Ryanair must repay about €9.6m in illegal state aid it received for its operations in several French regional airports.
The Commission, the European Union's executive arm, said Ryanair would have to repay €868,000 related to rebates and marketing arrangements negotiated at Angouleme airport in central France.
Ryanair had enjoyed "an undue advantage" and should repay the money so as to "remove the distortion of competition," the Commission said in a statement.
Similar findings at Pau Pyrenees airport required a repayment of €2.4m with €6.4m repayable at Nimes airport, both in southern France, it said.
The Commission said it was continuing an investigation into Austria's Klagenfurt airport where airport service and market agreements "appeared to be excessively favourable to Ryanair and therefore could involve incompatible state aid."
Probes into three German regional airports - Dortmund, Leipzig/Halle and Niederrhein-Weeze, where Ryanair is the largest client - found no problems with state-aid payments, it added.
Ryanair welcomed the Commission's decision in relation to these airlines and said they were consistent with its previous rulings on other locations.
It noted the decision relating to Angouleme, Pau and Nimes but said all of its airport arrangements comply with European state aid rules.
"Ryanair has therefore instructed its lawyers to appeal these rulings to the extent they erroneously allege otherwise," the airline said.