Ryanair is to launch an immediate appeal to the European Court in Luxembourg after hearing that the European Commission is likely to find parts of its arrangements at Brussels Charleroi unlawful.
The low fares airline will also enter into negotiations with both Brussels Charleroi and the Walloon Government to explore the possibility of the airport being privatised and a long term, low cost arrangement being put in place to continue its operation there.
If neither option is successful the company will be forced to close its base there.
It would then be forced to transfer the aircraft and the routes to another privately owned European capital city airport.
Speaking today, Ryanair chief executive Michael O'Leary said: "Why should a complaint from the state owned, high cost Brussels Zaventem Airport be allowed defeat competition and low fares?
"Ordinary consumers will be mystified that the Commission would rule against Charleroi just because it is State owned, when many other privately-owned airports are free to enter these deals.
"A negative decision by the Commission in this case will be manifestly in error and will do untold damage to the growth of low fare air travel and competition in European air transport," O'Leary added.
Two million passengers per year pass through Ryanair's Charleroi base.