Deutsche Lufthansa ground staff went on strike Wednesday, causing more than 1,000 flights to be canceled and exacerbating travel disruptions during the busy summer tourist season, Reuters reported.

The Verdi union has called for a strike until 06:00 local time Thursday to demand a 9.5% pay rise for about 20,000 workers.

The move forced Lufthansa to cancel almost all flights in Frankfurt and Munich for Wednesday.

Strikes and staff shortages have already forced airlines, including Lufthansa, to cancel thousands of flights and have caused hours of queues at major airports, disappointing holidaymakers looking to travel after COVID-19 shutdowns.

Verdi demanded a 9.5% pay rise in June, or at least €350 a month for 12 months, for about 20,000 workers who it says are hurt by inflation and overworked by shortages of staff at airports.

Lufthansa has offered an increase of €150 per month until the end of this year and another €100 from the beginning of 2023, plus a 2% increase from mid-2023, depending on the company's financial results.

The union rejected the proposal, saying it was not enough to compensate for skyrocketing inflation, which hit 8.2% in Germany in June.

Verdi and Lufthansa have already held two rounds of wage talks. The third is scheduled for August 3 and 4.