Ground staff at Deutsche Lufthansa have gone on strike to demand higher wages, forcing the airline to cancel thousands of its flights at Frankfurt and Munich airports, with many shipments expected to be delayed.

The strike action is the latest setback for European airports. Airlines have voluntarily canceled passenger and cargo flights or rescheduled them at less busy times to help cope with congestion caused by too many passengers and an understaffed aviation system.

Lufthansa said it had to cancel 32 flights at Frankfurt Airport on Tuesday and 646 on Wednesday, as well as 345 flights at Munich airport, affecting 132,000 passengers and reducing belly capacity.

Lufthansa spokeswoman Jacqueline Casini said: "We are monitoring the situation closely and taking steps to maintain cargo operations in the best possible way for our customers." We are in close communication with all relevant parties to avoid delays or flight cancellations. But it is difficult to estimate how many Lufthansa Cargo ground staff will respond to the strike call."