Many French flights will be disrupted throughout Monday as air traffic controllers carry out a fresh one-day strike.
Up to a quarter of trips could be cancelled at the four airports affected - Paris-Orly, Toulouse-Blagnac, Bordeaux-Mérignac and Marseille-Provence.
The strike began at 6pm on Sunday and is expected to carry on throughout the whole of Monday.
Flights have to be cancelled for safety reasons, because air traffic control is only operating at a limited service, the French Civil Aviation Authority said.
The agency said: “Despite our preventative measures, passengers should still expect delays.
“Passengers who are able to travel at a later date should do so.”
Some 25 per cent of journeys to and from Paris-Orly and Toulouse-Blagnac will be axed, according to French media.
Slightly less, 20 per cent, will be cancelled going to and from Bordeaux-Mérignac and Marseille-Provence.
The industrial action is a response to a law restricting air traffic controllers’ ability to go on strike being passed on November 15.
Under the new legislation requires the workers to register their intent to go on strike at least 48 hours before.
Before, individual air traffic controllers did not have to inform their employers when they were planning to take part in walkouts - although unions did have to give notice.
Between 2004 and 2016, French air traffic controllers accumulated 254 days of strike action.
