BERLIN (AP) — More than 1,000 security personnel walked off their jobs Monday at airports across Germany, leading to dozens of flight cancellations and delays.

Security staffers at airports in Berlin, Dusseldorf, Hannover and elsewhere began their one-day strike at midnight to press for higher wages, German news agency dpa reported.

The walkouts are part of a wage dispute between Verdi union 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.

Verdi announced it also planned walkouts Tuesday at passenger controls at airports including Frankfurt, Hamburg, Stuttgart and Karlsruhe/Baden-Baden. At Germany’s largest airport, in Frankfurt, only passengers with layovers will be able to go through security checks Tuesday, a Verdi spokesman said, according to dpa.

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.

Verdi is demanding an increase of hourly wages by at least one euro, among other things.

The union said about 1,350 employees nationwide were participating in the strikes, dpa reported.