French air traffic controllers have walked out on strike causing disruption for thousands of passengers.
The walkout is the latest move but controllers in their campaign against plans to create a single European air traffic control system.
Unions argue the move could cost jobs.
French controllers decided to press ahead with the strike, despite the lack of support from European colleagues, and will also join a national stoppage of public service workers in France on Tuesday.
Easyjet said it was planning 56 cancellations across its European network, while Ryanair warned of delays.
British Airways has cancelled two Heathrow flights, one to Marseille and the other to Lyon.
Underpinning the dispute are plans for a Single European Sky.
The project is aimed at ending the current patchwork system which sees flights passed from one country’s air traffic control to another.