Cabin staff at German airline Lufthansa extended their strike action to three main airports on Tuesday, causing disruption with the cancellation of scores of flights.
The UFO union, which held a first strike at Frankfurt airport over pay and conditions on Friday, said it was staging fresh walkouts at airports in Berlin and Munich as well as Frankfurt.
The strike began at 3am GMT at Berlin-Tegel airport, one of two serving the German capital, and an hour later at Frankfurt airport, the third busiest in Europe, with the stoppages due to last eight hours.
Cabin crew will also go on strike from 11am GMT to 10pm GMT in Munich, the union said.
A Lufthansa spokesman said a total of 180 long and short-haul flights had been cancelled at Frankfurt airport, its main hub, and flights in Germany and Europe had also been cancelled in Berlin.
The union, which represents some two-thirds of Lufthansa's 18 000 cabin crew members, has vowed that the latest strike would have an even bigger impact than Friday's action.
A total 26 000 passengers were affected by last week's eight-hour stoppage at Frankfurt airport in western Germany where nearly 200 Lufthansa flights were grounded.
Lufthansa and UFO traded verbal blows early on Tuesday, each accusing the other of arrogance.
UFO head Nicoley Baublies warned on the N24 news channel that the strike could be widened out if an accord continues to prove elusive, cautioning it could announce in the coming days that "Germany comes to a standstill for 24 hours".
For its part, the airline criticised the labour union for announcing the start of the strikes at the three airports late.
The strike was called after Lufthansa's management failed to come to an agreement with employees over salary and working conditions.
UFO is seeking a five percent pay increase for cabin staff backdated to January after three years of wage freezes.
It is also opposed to the use of temporary cabin staff on Lufthansa aircraft.
A Lufthansa spokesman said on the ntv news channel on Tuesdsay that the airline had offered a salary hike of about 3.5 percent as well as renouncing fixed-term contracts and the use of temporary staff.
"UFO has not given us a contribution towards increasing competitiveness," such as, working an extra two hours a month, he complained, calling for the parties to return to the negotiating table.
A Lufthansa spokesman had said the airline would do everything possible to minimise disruption to travellers, with passengers informed about developments by email or text message.
The airline already faces strong headwinds from rising fuel prices and fierce competition.
An earlier strike by cabin crew at the beginning of 2009 cost Lufthansa tens of millions of euros.
And it is not the first time this year that Lufthansa has felt the pinch from industrial action.
In February, Frankfurt airport's apron control staff, traffic controllers who guide aircraft while they are on the tarmac, walked off the job over demands for higher pay.
Ed's note: Lufthansa services to South Africa are currently not affected by the strike, although passengers with onward connections should reconfirm their flight with the airline before departure.