Air France announced that 90 percent of flights from Paris' Charles de Gaulle airport would not be interrupted but around 50 percent from Orly would risk cancellation.
Besides, as air traffic controllers are planned to join the 24-hour strike, the French Civil Aviation Authority also limited flights, affecting many airliners to France.
The French government is pushing to raise the minimum retirement age from 60 to 62 in 2018 and prolong the full pension retirement age to 65. Despite a long campaign for the reform, most workers didn't buy the plan.
Union organizers expected to mobilize at least 2 million people to demonstrate across France as the reform bill is due to be presented to parliament for debate on Tuesday night.
"The only chance today ... to change the reform... is to be numerous in the street on Tuesday," Francois Chereque, leader of one major union CFDT, told France 24 television.
Many public servants, postmen, workers with energy supplier EDF and hospital servicemen will also take part in the walk-out.
A weekend poll showed that over 50 percent of French people support the pension reform, but another poll by Ifop for Ouest France indicated that 70 percent of the citizens support the strike.