Ground staff for Lufthansa walked off the job at five major German airports on Wednesday, causing the airline to cancel hundreds of flights.

The Ver.di union called on ground staff at Frankfurt and Munich, Lufthansa’s two main hubs, as well as Berlin, Duesseldorf and Hamburg, to strike for 27 hours starting at 4am  on Wednesday.

Lufthansa said ahead of the strike that it expected to be able to operate around 10-20% of all planned flights. It said tickets could be rebooked free of charge, while tickets for German domestic flights could be converted to rail vouchers.

In Frankfurt, the company cancelled 80-90% of a planned 600 departures and arrivals by Lufthansa itself and its subsidiary Air Dolomiti. More than 400 departures and arrivals at Munich Airport were also cancelled.

All Lufthansa departures from Berlin and Hamburg were cancelled, as were most domestic flights from Duesseldorf.

Lufthansa anticipated that, in all, more than 100 thousand people would have to change their travel plans.

Lufthansa unit Eurowings said it wasn’t affected.

The union is seeking a 12.5 per cent pay raise, or at least 500 euros more per month, in negotiations for nearly 25 thousand employees, including check-in, aircraft handling, maintenance and freight staff.

Hours-long or one-day “warning strikes” are a common tactic in German contract negotiations.

Coinciding contract negotiations have resulted in several recent walkouts in the rail, air and local transport sectors, making for a frustrating few weeks for travellers and commuters in Germany.