Air France anticipates it will cut its number of flights by about one-half during the pilots’ strike currently called for Sept. 15-22, according to Frederic Gagey, the chairman and CEO of the French subsidiary of Air France KLM SA (EPA:AF). Gagey said on France Inter radio Saturday that the walkout would cost his unit between €10 million ($12.96 million) and €15 million ($19.44 million) a day, Reuters reported.

“On the basis of what we have now, I think we shall only be able to operate roughly 50 percent of flights,” Reuters quoted Gagey as saying on air. “The passengers will be informed, and we ask them, if possible, to change their tickets to avoid this period, which is a little uncertain.”

Europe’s No. 2 traditional carrier by revenue said this month it would proceed with a plan to open new bases in Europe under the Transavia brand to recapture market share from low-cost carriers and Middle East rivals. The pilots’ unions are not on board with this plan, which is one reason cited for the looming one-week strike.

The airline has indicated it would negotiate on benefits linked to seniority and incentives for Air France pilots who transfer to Transavia, but that it would not yield to unions demanding that the collective-bargaining agreements of pilots flying under the Transavia brand carry the same terms as those flying under the Air France brand, Reuters said.

Air France has advised its customers with bookings on flights during the walkout period to either change their tickets or postpone their trips at no extra cost. They can contact the airline to do it in multiple ways, including by calling its toll-free numbers 0800 240 260 (in France and the French overseas departments) and +33 1 57 02 10 58 (elsewhere) or by visiting its online site.