But on Friday, the Verdi trade union plans to bring seven German airports to a standstill with a warning strike. Hundreds of thousands of passengers will be affected, as the ADV airport association fears. It expects that a large part of domestic and international air traffic will not take place. The airports in Frankfurt, Munich, Stuttgart and Hamburg announced that they would suspend regular passenger operations on Friday.

The ADV warned of "massive disruptions in air traffic". The warning strike will lead to around 2,340 flight cancellations in domestic and international air traffic, the association announced. "More than 295,000 passengers are becoming a pawn in Verdi's strike tactics," the ADV criticized, speaking of an "unprecedented escalation."

Fraport airport services said regular passenger operations would not be possible on Friday at Germany's largest airport in Frankfurt because of the warning strike. An exception would be made for emergency flights. In Frankfurt alone, 1,005 departures or arrivals had been planned for Friday. The airport spoke of 137,000 passengers being affected. It urged passengers to not come to the airport and to get information from their airline. "Passengers who want to start their journey in Frankfurt will not be able to get their flight." Transfer traffic was also expected to be affected.

Lufthansa will have to cancel about 1,200 flights in Frankfurt and Munich on Friday, a spokesperson said. The number as of Wednesday evening was expected to increase, he added.

Cologne/Bonn Airport advises passengers who want to fly to Munich or Hamburg on Friday to inquire with the airlines about possible flight cancellations. At Wahn Airport, this could affect connections to Munich and Hamburg. Other airports for which Verdi has called a strike are those in Frankfurt, Stuttgart, Dortmund, Hanover and Bremen.

A spokesman for Cologne-Bonn Airport was unable to provide more precise information on Thursday morning. It is the responsibility of the airlines to inform passengers about possible flight cancellations, the spokesperson stressed. Passengers should inquire with their airline to be sure.

Verdi had announced that it would strike at the airports for the entire day on Friday. The warning strike is to begin early Friday morning and end some time at night. Relief deliveries to earthquake victims in Turkey and Syria are to be exempt.

With the warning strike, employees want to underscore their demands in the collective bargaining dispute with the federal and municipal public service. Besides the public sector, there are local negotiations for ground handling services and a nationwide round of collective bargaining for aviation security.

The warning strike is taking place at the start of the Munich Security Conference, which is considered the most important meeting of politicians and experts on security policy worldwide and runs from Friday to Sunday. Munich Airport emphasized, however, that flights for the Munich Security Conference are exempt from the suspension of regular passenger operations in Munich. The security conference is working to be able to guarantee the arrival of participants, it said Wednesday.

In the collective bargaining dispute, Verdi and the civil servants' association dbb are demanding 10.5 percent more income, but at least 500 euros more for the approximately 2.5 million employees of the federal and local governments. The term is to be twelve months. The employers have rejected the demands. The second round of negotiations is scheduled for February 22 and 23 in Potsdam.

There had already been delays and cancellations for tens of thousands of passengers flying from Frankfurt on Wednesday. A cable that was cut during construction work led to a breakdown in Lufthansa's computer systems.

(Original text: dpa, Ulla Thiede / Translation: Carol Kloeppel)