Frankfurt: Tens of thousands of Lufthansa passengers faced disruptions on Thursday as cabin crew in Germany kicked off a "massive" 48-hour walkout in the biggest escalation yet of a bitter row over pay and conditions.
The strike called by Germany's UFO flight attendants' union was scheduled to start at 2300 GMT on Wednesday and last until 2300 GMT on Friday.
Lufthansa said it was forced to scrap 700 flights on Thursday and some 600 the following day, warning that "around 180,000 passengers will be affected".
The UFO union said the stoppage would impact all Lufthansa departures from German airports.
Last-minute efforts by Germany's largest airline to halt the strike failed after a court in Frankfurt on Wednesday confirmed that the walkout was legal.
Lufthansa said it regretted the inconvenience caused to passengers and stressed that the group's other airlines were not affected.
"We will do everything we can to minimise the impact of this massive strike on our customers," a spokesman told AFP.
The carrier said it would run an alternative flight schedule where possible, and that passengers could rebook their journeys for free or swap their flights for train tickets.
The UFO union argued that the stoppage was necessary because negotiations with Lufthansa bosses were deadlocked.
UFO vice-president Daniel Flohr warned that further strikes could come "at any time". The walkout is seen as a test of strength for the union after months of infighting.
It is also UFO's biggest call to action since a week-long strike in 2015 hit Lufthansa with mass cancellations.
The union already staged a day-long warning strike last month at four Lufthansa subsidiary airlines, causing several dozen flights to be axed at Eurowings, Germanwings, SunExpress and Lufthansa CityLine.
But the flagship Lufthansa brand was spared the upheaval after management offered a surprise two-percent pay rise to avert the strike.
Since then, however, UFO's Flohr said no progress had been made in talks. As well as higher pay for cabin crew across the Lufthansa group, UFO is demanding more benefits and easier routes into long-term contracts for temporary workers.
Lufthansa for its part has argued that UFO does not have the right to represent staff anymore following an internal leadership tussle, and has challenged the union's legal status in court.
The internal disputes have cost the union support among the Lufthansa group's 21,000 flight attendants, with some members switching to rival unions.
"UFO is battling for its life," the Handelsblatt business daily wrote last month.