Around 200 workers at Frankfurt Airport, Europe's third-busiest, have gone on strike over pay, forcing 150 flights to be cancelled and risking Europe-wide air travel disruption.
In the first of two planned days of warning strikes, the airport's so-called "apron control" staff - who direct aircraft in and out of their parking positions - halted work at 3pm yesterday (3am today NSZT).
Of the 1250 flights planned for today, 150 had been cancelled as of the afternoon, according to an official of Fraport, the company which owns and operates Germany's biggest airport.
Initially, the GdF air traffic workers union had planned only one day of action, until 10pm yesterday.
But it was decided to repeat the strike again from 8am until 10pm today to increase the pressure on Fraport.
The move was heavily criticised not only by Fraport itsef, but also industry federations BDL and BDI.
"Our contingency plans for tomorrow are ready and we've sufficient personnel to handle more than 50 per cent - at the very least - of flight operations," Fraport board member Peter Schmitz told reporters.
"And I'm optimistic that, following the learning curve that our employees surmounted today, we'll succeed again tomorrow," Schmitz said.
A Fraport spokesman advised passengers to contact airlines directly, since it was primarily up to them to decide which flights would take off or land.
The company had trained up other staff to take over the duties and tasks of the striking workers, spokesman Mike Schweitzer said.
"And former colleagues who used to work in this area have also said they would jump in," Schweitzer added.
"We will ensure that flight safety is guaranteed."
German carrier Lufthansa, which has its main hub in Frankfurt, said it would cancel as many as 100 flights out of a total 316 taking off or landing yesterday.
So far, only flights within Europe had been affected, with all long-haul flights going ahead, a spokeswoman said.
Travellers seemed resigned to having their travel plans disrupted, with some voicing sympathy over the strike action.
Svein Marco Roszkowski, who had just flown in from Chile with his sister Jenniffer and two children, said their onward flight to Oslo had been delayed for five hours.
"That's life. I guess people have a reason to strike," Jenniffer said.
Jan Bucher of Germany, who was headed for Athens, said: "I have a two-hour delay. But I have an understanding for the strike."
The wage dispute concerns some 200 personnel, including workers in the actual air traffic control centre, as well as those working on the airport tarmac. The GdF union called for warning strikes after Fraport turned down mediation proposals in their wage dispute.
The union argues that apron controllers' pay does not take into account the additional complexity resulting from the opening late last year of a fourth runway in Frankfurt.
Fraport denounced the action as "irresponsible" and "incomprehensible" and the industry federation BDL similarly slammed it as "unacceptable".
"That just 200 out of 20,000 people who work at Frankfurt airport want to paralyse the entire operation is unacceptable," BDL chief Klaus-Peter Siegloch said in a statement.
"This tiny group is taking tens of thousands of passengers hostage for their pay demands. The strike will lead to delays and cancellations for passengers beyond Frankfurt, as the entire European flight network will be affected," Siegloch said.
A board member of the powerful BDI industry federation, Dieter Schweer, said the strike would damage the whole economy.
"It is irresponsible and totally out of proportion," he said.
"It is not acceptable that small groups in key functions paralyse critical infrastructures to push through their own individual interests."
National rail operator Deutsche Bahn said it would lay on extra trains and staff to cope with the large number of passengers expected to travel by train instead.
Airlines Lufthansa and Air Berlin were offering passengers free rail vouchers for travel to destinations within Germany.