Lufthansa, Germany's largest airline, said it had cancelled around 600 flights - about a third of its services - due to a planned strike by public-sector workers across the country's airports.
Trade union Verdi has called on ground staff, baggage handlers and maintenance staff at almost all of Germany's big airports, including Europe's third largest hub at Frankfurt, to strike during the morning shift on Thursday, which runs until around 1300 GMT (1am Friday NZT).
The union's aim is to increase pressure on the government ahead of a third round of pay talks due to start at the end of the month. The walkout is part of wider industrial action that has also seen strikes by a range of other public-sector workers, including local transport staff and childcare workers.
Lufthansa, which typically operates around 1,800 flights on a Thursday under its Lufthansa and Germanwings brands, said it was cancelling almost all of its domestic flights that were due to take off before 1300 GMT. Long-haul flights would also be affected, it said.
The union says it expects around 1,400 people to take part in the strike action at Frankfurt airport alone.
The strike will affect Cologne-Bonn, Duesseldorf, Hamburg, Hanover and Stuttgart airports, as well as Munich and Frankfurt.
Other airlines that said passengers could expect delays and cancellations include holiday specialists TUIFly and Condor, as well as Air Berlin, Germany's second largest airline.
Lufthansa said the strike would cost it millions of euros. A walkout last month by security staff at Frankfurt airport, which brought chaos to the terminal as people were unable to get through security checks, cost the carrier €3 million (NZ$4.8 mllion) in operating profit.
This time, Lufthansa said it and airport operator Fraport would try to better manage the expected queues by dividing the terminal into different coloured zones for different services.
Customers may also rebook tickets free of charge or those on domestic flights can instead travel on the Deutsche Bahn network of high-speed trains, the company said.
Trade unions want pay rises of 3.5 per cent plus an extra €100 ($160) per month for about 2.1 million federal and municipal public sector workers. That would amount to a total increase of 6.7 per cent, they say.
The government says it is willing to accept a pay increase but that the demands are too high.