Ryanair chief executive, Michael O’Leary has vowed to appeal today's European Commision decision on Charleroi to the European Court.
Speaking a short time ago, O'Leary said: "This decision will be appealed to the European Court.
"We believe the appeal will be supported by many other low fares airlines, regional airports and consumer groups.
"Charleroi airport was empty five years ago. Both Brussels Charleroi and Ryanair are profitable at these discounted rates, and 2.5 million consumers annually now fly to /from Brussels Charleroi at the lowest fares in Europe thanks to these discounted routes.
"The only beneficiaries of this decision is the original complainant, Brussels Zaventem Airport and the high fare carriers who fly there.
"They will now face reduced competition, and higher fares at Brussels Charleroi, thanks to the failure of the EU Commission to promote competition, lower fares and consumer interests," he added.
Earlier, the European Commission said Ryanair should repay around €4.5m of the subsidies.
Analysts believe that Ryanair may be forced to increase its prices to combat this decision.
Shares in the company were trading at €5.13 - up 47c - before lunchtime.