Germany's Lufthansa will cancel some 3800 flights because of a three-day strike by the pilots' union later this week, hitting more than 425,000 passengers.
The cancellations include domestic and intercontinental connections on Wednesday, Thursday and Friday, the airline said.
"A strike of three consecutive days would be one of the biggest walkouts in Lufthansa's history," the company wrote in a statement.
A union representing pilots at Lufthansa called for the strike last week in a long-running pay dispute. Among other issues, the Vereinigung Cockpit union said Lufthansa had failed to make a "negotiable offer" during two years of pay negotiations.
Though the strike starts on Wednesday, some Tuesday flights have been cancelled for logistical reasons.
Lufthansa, Lufthansa Cargo and the company's budget airline Germanwings are all affected.
Passengers were being informed about the cancellations by text messages and emails, Lufthansa said.
The airline tried to rebook their customers onto other airlines and offered them the opportunity to use their plane tickets on trains in Germany instead.
Lufthansa said the strike would cost the airline tens of millions of euros.
Lufthansa had to cancel hundreds of flights last week when public-sector workers went on strike at seven German airports in a dispute that had nothing to do with the airline.
Lufthansa has been trying to cut costs amid tough competition from European budget carriers and aggressively expanding government-owned Gulf airlines.