Ryanair has canceled more than 250 flights to France due to a planned strike by French air traffic controllers.
Further cancellations are likely, the low-cost airline warned.
The SNCTA union of air traffic controllers told the French Civil Aviation Authority (DGCA) that the strike would take place on April 8 and 9.
“Disruption is expected over the whole country,” the DGCA said.
The Authority has asked airlines to cut their schedules for flights to and from France on April 8 by 40%.
The SNCTA says it is unhappy about offers made by the state on new working conditions and retirement plans.
“We sincerely apologize to all customers affected by this unwarranted strike action and we call on the EU and French authorities to take measures to prevent any further disruption,” said Ryanair in a statement.
“It’s grossly unfair that thousands of European travelers will once again have their travel plans disrupted by the selfish actions of a tiny number of French ATC [air traffic control] workers.”
Ryanair is offering to transfer customers’ tickets to other flights or provide refunds.
Air France says that it expects to operate almost all its long-haul flights and 60% of its medium-haul flights to and from Paris Charles de Gaulle airport.
Travelers booked on short- and medium-haul Air France flights on April 8 or April 9 can choose to travel between April 10 and April 15 instead, it said.
“Expect cancellations and major delays,” warned the European Organization for the Safety of Air Navigation on Twitter.