Budget carrier Ryanair and British Airways owner IAG said Wednesday they will file a complaint to the EU over what they say is France's failure to tackle crippling strikes by air traffic controllers.
They say repeated strikes by French controllers, particularly in Marseille, are having a devastating impact on schedules, with more than 750,000 passengers having flights cancelled in the first five months of 2018 alone.
IAG chief executive Willie Walsh said passengers were being denied their right to free movement, which is enshrined in EU law.
"Both Ryanair and IAG plan to submit a complaint to the European Commission which will be against the French government because we believe that the French government is not adequately protecting the rights of Europeans to free movement," Walsh told a news conference in Brussels.
The overwhelming majority of passengers affected are not flying to or from France, he said, but travelling on routes which pass through French air space.
This means that if French controllers are on strike, their flights have to take longer routes to avoid flying through.
Michael O'Leary, Ryanair's outspoken chief executive, said 2018 was on course to be the worst year ever for controller strikes, with 28 days lost already.
"You can't have the freedom of movement if a couple of hundred air traffic controllers in Marseille are going to shut down the skies over Europe on a regular basis," he told reporters.
Fresh misery for travellers lies in store this weekend, he said, with Marseille controllers due to go on strike again and Ryanair asked to cancel 180 flights on Saturday and Sunday -- only 10 of which are taking off or landing in France.
The Marseille control zone is a particular problem because it covers part of the western Mediterranean that many flights from Barcelona and the Balearic Islands -- major tourist destinations -- pass through.
Walsh and O'Leary said they were disappointed at the lack of action from the European Commission, the bloc's powerful executive arm.
They called for air space above a certain height to be designated as European, so that planes flying over an area affected by a controller strike could be managed by authorities in neighbouring zones.
The suggestion was originally tabled by the commission, they said, but has not been acted on yet.
A French senate report this week said the country's air traffic control was responsible for a third of all aviation delays in Europe, according to Le Parisien newspaper.
Between 2004 and 2016, French air traffic controllers were on strike for 254 days, vastly outstripping their closest rival Greece, where there were 46 days of stoppages and Italy with 37, according to the report seen by the daily.