The French Civil Aviation Authority has told airlines they need to cut 40 per cent of flights today (Wednesday) due to strikes by French air traffic controllers.
Ryanair has already cancelled over 250 flights and warned further cancellations and delays are likely.
The airline said the strike was ‘unwarranted’ and called on the EU and French authorities to take measures to prevent any further disruption.
"It’s grossly unfair that thousands of European travellers will once again have their travel plans disrupted by the selfish actions of a tiny number of French ATC workers," it said.
All customers have been contacted by email and text message and advised of their options – a full refund, free transfer onto next available flight or free transfer onto an alternative flight routing.
EasyJet has cancelled 118 flights to and from France, including 10 to and from the UK, and is also keeping passengers informed of any flight changes via e-mail and text.
"Customers can also check flight information on our Flight Tracker page on our website," it said.
Air France has cut 40% of its medium-haul flights from Paris Charles de Gaulle, 70% from Orlay, and 40% of flights from other French airports.
It said it will operate nearly all of its long-haul schedules.
Air France said last-minute delays and cancellations can also be expected and is strongly advising customers to rebook alternative flights from April 110.
It also advised passengers to update their contact details on its website with their telephone numbers or email address so it can keep them updated.
British Airways would not disclose numbers, but said it would be using larger aircraft as well as re-routing some flights to try ‘to help as many customers as possible get to where they need to be’.
"Unfortunately there will be some knock-on delays to other parts of our short-haul network as a result of the strike action, given how much airspace in Europe will be affected. We are sorry for the disruption to customers’ travel plans," it added.
The SNCTA is planning nine full days of strikes between April 8 and May 2, starting with a 48-hour walk-out.
Short-haul flights to and from France are most likely to be hit.
But even passengers flying to and from other European destinations, with flight paths over French airspace, are likely to be impacted.
French airspace is the busiest in Europe, with an average of 8,000 flights each day.
The strikes could cause disruption for thousands of British holidaymakers returning from their Easter breaks.
