German airline Lufthansa said it will cancel 290 flights Friday, the first day of a planned week of walkouts by cabin staff in a long-running dispute over cost-saving measures.
Some 37,500 passengers would be hit by the nine-hour strike scheduled to begin at 1300 GMT and affecting the Frankfurt and Duesseldorf airports, Lufthansa said in a statement.
The 290 cancelled flights include 23 inter-continental services, the statement said.
Lufthansa subsidiaries Germanwings, Eurowings, Lufthansa CityLine, SWISS, Austrian Airlines, Air Dolomiti and Brussels Airlines were expressly not targeted by the industrial action.
Lufthansa said it "regretted" the decision by the flight attendants' union UFO to stage a walkout between 1300 GMT and 2200 GMT at the Frankfurt and Duesseldorf airports.
It apologised to passengers, but said the short notice of the strikes made it difficult to inform passengers in time and enable them to make alternative travel arrangements.
"We will do everything possible to keep disruption to a minimum," it said.
The union plans to stagger the walkouts and target different airports over the course of the next seven days, with a repeat of the stoppages planned in Frankfurt and Duesseldorf on Saturday.
However, Lufthansa's Munich hub would not be affected at all this weekend, given that there were still school holidays in the southern regional states of Bavaria and Baden-Wuerttemberg, it explained.
In addition, "no industrial action is planned at all on Sunday since most people travelling that day will be doing so in a private capacity," UFO said.
UFO had announced on Thursday that industrial action was "unavoidable" after management had failed to come up with an improved offer in a long-running dispute over pay and early retirement provisions.