Air travel has been disrupted across Germany as security personnel at several airports in the country staged walkouts as part of their demands for higher wages.

Numerous flights were cancelled at Frankfurt Airport due to the strike organised by trade union ver.di, the German news agency dpa reported.

Starting at 2am (1am GMT), employees of the cargo and passenger controls at Germany’s largest airport stopped working, a ver.di spokesperson said.

Only passengers with connections were able to go through security checks in Frankfurt.

Airport operator Fraport had called on all travellers hoping to board in Frankfurt not to travel to the airport.

According to Fraport, 130 of 818 flights planned for Tuesday were cancelled. Originally, about 71,000 passengers had been expected at the airport that day.

Employees at Hamburg, Stuttgart and Karlsruhe/Baden-Baden airports also walked out of their jobs. In Munich, Germany’s second-largest airport, a walkout has been under way since Monday afternoon.

Other airports including Berlin, Dusseldorf and Hanover cancelled dozens of flights on Monday due to one-day strikes there.

The walkouts are part of a wage dispute between ver.di and the Federal Association of Aviation Security Companies.

The union is negotiating with the employers’ association for a new agreement for about 25,000 security staff nationwide.

Ver.di is demanding an increase in hourly wages of at least one euro, among other things.

Three rounds of negotiations have so far failed to produce a result. The sides plan to meet in Berlin later this week for further negotiations.