Hundreds of flights to and from France were expected to be cancelled Wednesday as air traffic controllers launched a two-day strike over working conditions.
The civil aviation authority has asked airlines to scrap around 40 percent of flights, warning of "disruption across the whole country."
Flag carrier Air France warned of "very severe disruption" to its flight schedule. Although it pledged to operate "almost all" long-haul flights, medium and short-haul services would be badly affected, it said.
"We cannot rule out last-minute delays and cancellations," the airline added.
Low-cost operator Ryanair said it had been forced to cancel more than 250 flights due to the industrial action.
"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 ... workers," the Irish airline fumed.
Passengers had been warned well in advance and seemed to have made other plans. The situation in Paris terminals was relatively calm.
"The companies have done what was needed. For the moment, there are no difficulties," one airport source said.
The strike was called by the main air traffic union SNCTA, which wants talks over the specific working conditions of their members.
A particular bone of contention is the pushing back of the retirement age for air traffic controllers from 57 to 59.
The union insists that for the past 10 years, talks over working conditions have taken place outside the formal structure for union-management negotiations.
The FNAM aviation association strongly criticised the strike, saying it would "essentially penalise French-based airlines and their sub-contractors."
Transport Minister Alain Vidalies "regretted" that the union had chosen to call for strike action and noted that a meeting was due to take place on April 13 to discuss the specific working practices in the sector.
The SNCTA had originally called the strike from March 25 to 27 but scrapped it after the Germanwings crash in the French Alps that killed 150.
Further industrial action is planned from April 16 to 18 and from April 29 to May 2, key holiday periods.