About 180,000 Lufthansa passengers are due to be affected by 1300 flight cancellations on Thursday and Friday due to industrial action by the Independent Flight Attendants Organization.
Germany's largest airline said it "regrets the inconvenience for the passengers".
Lufthansa canceled 1,300 out of 6,000 flights scheduled - 700 on Thursday and 600 on Friday.
Cabin crew members have received court approval for an 48-hour long strike at German flag-carrier Lufthansa.
Lufthansa said that passengers traveling on cancelled flights could rebook online, or convert their flight to a train ticket for domestic flights.
Lufthansa is promising to release a "special flight schedule" to reduce the impact on passengers and is offering free rebooking even for passengers whose flights have not been cancelled.More news: Sons failed tech bets behind Softbank Groups $6.5 billion quarterly loss
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The court ruled that the strike was legal.
The UFO union has said the strike was necessary because negotiations with Lufthansa bosses were deadlocked. The airline has cancelled around 1,300 flights for Thursday and Friday.
Lufthansa lost a bid to halt the strike at a Frankfurt labour court earlier on Wednesday but the company is appealing with a decision expected later in the day.
In addition to higher pay for cabin crew across the Lufthansa group, UFO is demanding more benefits and easier routes into long-term contracts for temporary workers.
The strike comes as part of an ongoing dispute between the airline and flight attendants about pay and working conditions, as well as the union's status - Lufthansa has been unwilling to recognize the union.
Months of infighting have cost the union members and support among cabin crew, some of whom have now turned to other representative organisations.