Some 150 Ryanair flights scheduled to and from Germany on Wednesday will be cancelled due to a strike by pilots and cabin crew, Ryanair Chief Marketing Director Kenny Jacobs said on Tuesday.
The strike is expected to affect Ryanair flights to and from Greece.
Verdi, the pilots and cabin crew union, called a 24-hour strike for better pay and working conditions which is scheduled to begin at 04:00 Greek time (01:00 GMT).
The strike follows coordinated action among pilots in August, which forced the company to cancel 400 out of 2,400 scheduled flights in Europe, during the high-travel summer season.
Ryanair, which handles close to 130 million passengers a year, has reached agreements with its staff in Ireland and Italy.