Lufthansa says it will have to cancel almost all flights at its main Frankfurt and Munich hubs on Wednesday because of a strike by its German ground staff, affecting tens of thousands of passengers in the latest travel turmoil to hit Europe.

The airline said Tuesday that the strike will force the cancellation of 678 flights at Frankfurt, 32 of them on Tuesday and the rest on Wednesday. It also is canceling 345 flights at Munich, including 15 on Tuesday.

Lufthansa said that 92,000 passengers will be affected by the Frankfurt cancellations and 42,000 by the Munich disruption. It said those affected will be contacted Tuesday and rebooked on alternative flights where possible but warned that “the capacities available for this are very limited.”

The company said the strike may still lead to “individual flight cancellations or delays” on Thursday and Friday.

The ver.di service workers’ union announced the one-day strike on Monday as it seeks to raise pressure on Lufthansa in negotiations on pay for about 20,000 employees of logistical, technical and cargo subsidiaries of the airline.

The walkout comes at a time when airports in Germany and across Europe already are seeing disruption and long lines for security checks because of staff shortages and soaring travel demand.

As inflation soars, strikes for higher pay by airport crews in France and Scandinavian Airlines pilots in Sweden, Norway and Denmark have deepened the chaos for travelers who have faced last-minute cancellations, lengthy delays, lost luggage or long waits for bags in airports across Europe.

Travel is booming this summer after two years of COVID-19 restrictions, swamping airlines and airports that don’t have enough workers after pandemic-era layoffs. Airports like London’s Heathrow and Amsterdam’s Schiphol have limited daily flights or passenger numbers.

The Lufthansa strike is set to start early Wednesday and end early Thursday. Such “warning strikes” are a common tactic in German labor negotiations and typically last from several hours to a day or two.

Ver.di is calling for a 9.5% pay increase this year and says an offer by Lufthansa earlier this month, which would involve a deal for an 18-month period, falls far short of its demands.

Lufthansa’s chief personnel officer, Michael Niggemann, argued that “this so-called warning strike in the middle of the peak summer travel season is simply no longer proportionate.”