Air traffic controllers in France were poised to go on strike Wednesday, likely leading to cancellation of some 40 percent of flights in French airspace.
"Disruption is expected over the whole country," said the DGAC civil aviation authority, which requested companies to scrap 40 percent of flights on affected routes as a preventative measure.
French flag carrier Air France said however that it planned to run "almost all" its long-haul services arriving in or departing from Paris on Wednesday.
But the airline said it planned to cut around 40 percent of its medium-haul flights.
The main air traffic controllers' union, the SNCTA, has also urged industrial action on April 16-18 and April 29 to May 2.
They are calling for talks over working practices and retirement age, currently set at 59 for air traffic controllers.
The SNCTA union had originally threatened to go on strike earlier but scrapped that industrial action in the wake of the Germanwings crash in the French Alps last month in which 150 people died.