Air France cut two-fifths of long-haul flights and half its other services on Friday as pilots began a four-day strike in a protest of the age of retirement.
The carrier expected some 80 percent of services at partner airlines Brit Air, CityJet, Regional, CCM and Airlinair to operate, it said in a statement on its Website on Friday, adding that regional unit Brit Air would be hit most.
Air France added that it could not rule out further last-minute flight cancellations.
"Air France is expecting very significant disruptions to its activities and apologises to all passengers for this situation, which it strongly deplores," the airline said in the statement.
The strike started at 2300 GMT on Thursday and is due to last until midnight local time on Monday and will likely cost the airline 100 million euros ($124.9 million), Chairman Jean-Cyril Spinetta said on Thursday.
Calling the protest over the retirement age "useless and dangerous", Spinetta said in an open letter to unions the strike could worsen the impact of an industry-wide crisis.
Air France is the French flag carrier network operated by Franco-Dutch airline group Air France-KLM.
Transport officials have warned of severe disruption at French airports over the weekend due to the strike, called by some unions over plans to increase the retirement age to 65.
Spinetta said the extension would be optional and pilots would still be able to retire at 60 if they wished.
He said European safety authority EASA would in any case soon increase the maximum pilot retirement age to 65 and that France would have to fall in line with this measure.