Numerous flights at Frankfurt Airport were canceled on Tuesday morning due to a warning strike by the Verdi union.
As of 2 a.m., employees of the freight and passenger controls at Germany's largest airport stopped work, as a Verdi spokesman said in the morning.
Employees of the emergency service in the transit area are excluded.
The warning strikes are part of the wage conflict between Verdi and the Federal Association of Aviation Security Companies (BDLS).
The union is negotiating with the employers' association about a new collective agreement for around 25,000 security forces nationwide, three rounds of negotiations had so far remained unsuccessful.
Employees in Hamburg, Stuttgart and Karlsruhe/Baden-Baden were also called upon to stop working.
A warning strike has been going on in Munich, Germany's second largest airport, since Monday afternoon.
The Frankfurt Airport website showed that many departures had already been canceled on Tuesday.
The airport operator Fraport had previously asked travelers who wanted to board in Frankfurt not to travel to the airport.
According to the Verdi spokesman, an emergency service has been set up for passengers who change trains in Frankfurt.
The collective bargaining partners want to meet on March 16th and 17th for further negotiations.
The union demands, among other things, an increase in hourly wages by at least one euro per hour and the adjustment of regional wages.