Pilots at flag-carrier Air France have walked out at the start of a week long strike.
The carrier is expected to run less than half of its flights during the coming days, as pilots protest against a transfer of jobs by the airline to a low-cost carrier.
Air France is urging passengers around the world to change or postpone travel.
Last week Air France said it would transfer much of its European operations to low-cost carrier Transavia in order to keep up with competition.
Chief executive Frederic Gagey told France Inter radio that the strike would cost the airline £10 million a day.
The airline said it would consider negotiation on benefits based on seniority for Air France pilots who agree to work for Transavia.
However, it said it would not agree to trade union demands that the contracts of Transavia pilots carry the same terms as those flying under Air France.
The changes at Air France are part of Perform 2020, a long-term strategy designed to improve efficiency at the airline.
A key part of the plan is the accelerated development of Air France-KLM in the European leisure market, under the Transavia brand, based on the two existing companies - Transavia France and Transavia Netherlands – and new bases to be created in other European countries.
By 2017, Transavia will rank among the leading low cost carriers in Europe, operating a fleet of 100 aircraft and carrying more than 20 million passengers.