Airlines are warning of disruption due to a strike by French air traffic controllers tomorrow (Tuesday).
The action, part of a wider general strike across the country, is set to affect flights to and from France and to other destinations using French air space.
British Airways said if the threatened strike goes ahead it would be forced to cancel some flights.
"Other short-haul flights may also experience some disruption, given how many flights from numerous European airlines would normally use French airspace each day," it added.
"We will be using larger aircraft, where possible, to help affected customers and are doing all we can to reduce the levels of disruption.
"Once we receive more information from the French authorities about the likely scale of the industrial action we will aim to finalise our Tuesday flight schedules by Monday afternoon."
BA has already relaxed its rebooking policy to help affected passengers.
Air France said the DGAC (French Civil Aviation Authority) has asked airlines to reduce their flight programme to and from Paris-Orly, Lyon and Marseilles airports.
"Disruptions are therefore expected on these destinations. Our flight schedule for 22 May 2018 has been updated. However, last minute cancellation or delays can be expected too," it said.
EasyJet is also expecting delays and cancellations due and advised customers to check the status of their flights.
"Please also be aware that public transport services will be affected by the strike. We recommend all customers allow plenty of extra time to get to the airport and consider alternative transport options where possible," it added.
