Lufthansa, Germany's biggest airline, on Friday cancelled 200 flights, affecting 25,000 passengers, ahead of a pilots' strike to be held later in the day.
The pilots' union Vereinigung Cockpit has called for a six-hour walk-out between 5:00 pm and 11:00 pm (1500-2100 GMT) over plans to change the airline's early retirement policy.
The industrial action is focussed on the country's biggest airport in Frankfurt and will ground most domestic and regional flights.
Lufthansa said individual flights would already be cancelled as early as 1:30 pm (1130 GMT) and most flights from 4:00 pm (1400 GMT).
The airline promised to try and minimise the impact of the strike for customers.
It said it had been able to inform most of the affected passengers on Thursday by publishing an emergency flight plan online and sending text messages to 14,000 passengers.
Lufthansa said it had reserved 2,200 hotel rooms in the Rhine-Main area as a precaution and both it and airport operator Fraport had set up some 500 field beds for passengers in transit who are not allowed to enter Germany for visa reasons.
Lufthansa staff would also hand out refreshments and snacks to passengers at the airport.
"We are mobilising all our capacities in order to minimise the effects of the strike on our passengers. This is very difficult on a Friday afternoon at the end of the school holidays in three German states, as this is one of the busiest travel days of the year," said board member Kay Kratky.
Lufthansa pilots can currently take paid early retirement from the age of 55. They are fighting a plan by the airline to raise the minimum age and to involve pilots in the financing of their pensions.
Last Friday more than 100 flights were cancelled at several of Germany's main airports as pilots of Lufthansa's low-cost airline Germanwings also walked out.
And on Monday, a union for German train drivers called for a three-hour walkout to turn up the pressure on management of the national rail operator Deutsche Bahn in gridlocked wage talks.