The cancellation is expected to get worse as the number of cancelled flights is expected to reach 20 per cent on Thursday.
Air France deplored the strike and added it was doing everything to limit inconvenience for passengers with some 20,000 set to be affected across the day.
Flights to destinations in Europe, North Africa and Israel will be affected, as well as some routes in Asia and Africa, the company said Monday.
Air France estimated that the stoppage would cost it around 40 million euros.
A spokesman added that Air France flights operated by low cost flyers HOP! And Transavia, as well as KLM Delta codeshares were not affected by the stoppage.
Unions representing around half of the strikers said the stoppage would go ahead as talks failed to bring a breakthrough on renewing an agreement on rules, pay and promotions which expires in October.
The management wants to limit the extension of the agreement to 17 months, whereas unions want between three and five years.
The CEO of the Air France-KLM group, Jean-Marc Janaillac, managed to put off a second pilots' strike in the month of June during the Euro football tournament.
The pilots' last strike, which grounded around 20 percent of flights, was from June 11 to June 14.