The action -- which began September 15 and was originally scheduled to last one week -- came in response to Air France’s plans to hire hundreds of new pilots on lower pay to fly for Transavia, a budget subsidiary.
The strike affected tens of thousands of passengers.
Financial Director Pierre-Francois Riolacci told reporters Wednesday that the €500 million figure takes into account lost revenue and any knock-on effect stemming from disgruntled passengers.
"We need a few more days to finalize completely our estimates, but we think the impact on the third quarter of 2014 will be in a range of €320 to €350 million," Riolacci said.
The Franco-Dutch company, Air France-KLM -- Europe’s second-biggest network carrier by revenue -- has said that the strike caused a fall of 15.9 percent in passenger traffic for the group in September, and 17.7 percent in cargo.
Meanwhile, bilateral meetings between the management of Air France and representative unions will be held today and tomorrow after the cancellation of a plenary meeting scheduled Tuesday to discuss the future of the low cost Transavia, according to daily Le Figaro.