More than 1,000 Lufthansa flights were canceled Wednesday as its German ground staff went on strike, affecting tens of thousands of passengers and adding to travel chaos during the busy summer season.

About 134,000 passengers had to change their travel plans or cancel them altogether. At least 47 connections had already been canceled on Tuesday, German news agency Deutsche Presse-Agentur (dpa) reported.

The ver.di service workers’ union had called for the walkout, which is due to run until 6 a.m. (4 a.m. GMT) on Thursday, over its demand for a 9.5% pay hike for around 20,000 workers.

Lufthansa's main hubs in Frankfurt and Munich were most affected, but flights were also canceled in Duesseldorf, Hamburg, Berlin, Bremen, Hannover, Stuttgart and Cologne.

The airline advised affected passengers not to come to the airports because most of the counters there would not be staffed anyway.

Strikes and staff shortages have already forced airlines including Lufthansa to cancel thousands of flights and caused hourslong queues at major airports, frustrating holidaymakers keen to travel after COVID-19 lockdowns.

Diego Lambiase, who was on his way from Africa to Paris, found himself stranded in Frankfurt on Wednesday when his onward flight was canceled.

"They say I will be rebooked tomorrow, but nobody was here when we arrived in order to say what we have to do, where we have to go, where we will sleep," he told Reuters TV at Germany’s busiest airport.

"We are looking for some Lufthansa people, but when we asked we were told it will be very hard to find someone from Lufthansa today at the airport. So we don’t know what to do," he said.

The airline said Tuesday that the strike would force the cancelation of 678 flights at Frankfurt, 32 of them on Tuesday and the rest on Wednesday. It also canceled 345 flights in Munich, including 15 on Tuesday.

Lufthansa said that 92,000 passengers would be affected by the Frankfurt cancelations and 42,000 by the Munich disruption. It said those affected would be contacted 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 cancelations or delays" on Thursday and Friday. Such "warning strikes" are a common tactic in German labor negotiations and typically last from several hours to a day or two.

Summer holiday ‘leverage’

Ver.di last month demanded a 9.5% pay rise, or at least 350 euros ($368) more per month for 12 months, for around 20,000 workers who it says are being squeezed by inflation and have been overworked due to staffing shortages at airports.

Lufthansa had offered an increase of 150 euros per month for the rest of this year and another 100 euros from the start of 2023, plus a 2% increase from mid-2023 dependent on the company's financial results.

Ver.di rejected the offer, saying it was insufficient to offset soaring inflation, which hit 8.2% in Germany in June.

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."

"I can understand (the strike) because they have the most leverage right now, during the summer holiday period," said Julian Grundmann, who was on his way to Seychelles on a different airline.

"But for everyone who wanted to fly today, who had been looking forward to their holiday for a long time, this is tough," he said.

Ver.di and Lufthansa have held two rounds of wage negotiations so far. A third is scheduled for Aug. 3 and 4.

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 cancelations, 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.