German airline Lufthansa is to cancel 3,800 flights on Wednesday, Thursday and Friday because of a strike by pilots over pay and working conditions.
The airline said 425,000 passengers would be affected by the stoppages.
It says that it has sent 100,000 text messages and emails to people who have booked on its flights in an attempt to prevent chaos at airports.
Emergency sleeping and food has been made ready at bigger airports for those who did not get the warning messages.
The BBC’s Steve Evans in Berlin says that the dispute over pay has been running for some months and the pilots’ union, Vereinigung Cockpit, feels it has been been getting nowhere.
VC argues that Lufthansa had failed to make a “negotiable offer” during two years of pay negotiations.
Lufthansa is increasingly competing with low-cost airlines across Europe.
Our correspondent says that what is not clear is whether the halting of Lufthansa flights will disrupt the wider European air-traffic system and cause delays for other airlines.
“A strike of three consecutive days would be one of the biggest walkouts in Lufthansa’s history,” the company said in a statement.
Lufthansa says that the dispute is likely to cost it tens of millions of euros.
Correspondents say that Lufthansa, Lufthansa Cargo and the company’s budget airline Germanwings are all affected by the strike.
The airline says that it is trying to rebook customers on to other airlines and has offered them the opportunity to use their plane tickets on trains in Germany instead.
Lufthansa had to cancel hundreds of flights last week when public sector workers went on strike at seven German airports in a separate dispute that had nothing to do with the airline.
This is the third strike to hit Frankfurt airport, Lufthansa’s home base, in six weeks.
The airline’s management is urging VC to restart negotiations as soon as possible.