Germany's national carrier Lufthansa canceled between 80% and 90% of its approximately 1,000 flights scheduled for Wednesday amid industrial action from ground crew.
While Germany's biggest hubs by passenger volume at Frankfurt and Munich are hardest hit, other airports — Hamburg, Berlin and Düsseldorf — will also be affected.
How will travelers be affected?
Lufthansa says more than 100,000 passengers will have to reschedule flights with most connections to and from Frankfurt and Munich canceled.
The airline has urged passengers booked on canceled flights not to go to airports because rebooking counters would not be staffed.
Lufthansa said it would be possible to convert domestic German flight tickets to vouchers for rail travel.
Travelers flying with Lufthansa subsidiaries and external airlines were expected to be largely unaffected. Lufthansa daughter airline Eurowings, for example, is planning to fly its full schedule.
At Munich and Frankfurt, short-haul crews were expected to prioritize services by Lufthansa's foreign subsidiaries Swiss, Austrian and Brussels Airlines.
Why is there strike action?
The walkout comes amid Lufthansa Group wage negotiations for some 25,000 ground crew employees at Deutsche Lufthansa, Lufthansa Technik and Lufthansa Cargo.
The staff rejected an employers' offer in the second round of negotiations on January 23.
Trade union Verdi wants a wage rise of 12.5% for staff, or at least €500 ($537) more per month over a 12-month-period. It is also demanding a one-time payment of €3,000 to offset the effects of inflation.
Widespread disruptions due to industrial action have hit German airports recently. Last Thursday, Verdi called for security staff at several major airports to take strike action.
There have also been strikes on Germany's railways and in other areas of public transport inflicting pain on the economy and creating a headache for German Chancellor Olaf Scholz's three-way governing coalition.