German airline Lufthansa says will cancel 3,800 flights this week because of a strike by pilots over pay and working conditions.
The airline said 425,000 passengers would be affected by the stoppages, due to take place on Wednesday, Thursday and Friday.
Lufthansa added it would inform passengers via text message or email about the flight changes.
Its freight carrier, Lufthansa Cargo, will also be affected.
Lufthansa said the impact on profits would be "in the range of tens of millions of euros".
"The announcement alone has already caused significant damages since passengers have already rebooked flights and logistic customers have made arrangements with other cargo airlines to secure the transport of their goods," it said in a statement.
"During the three-day walkout by Cockpit teams, there will only be around 500 short- and long-haul flights by Lufthansa and Germanwings," Lufthansa said.
However, the group said that pilots at its other airlines, including Swiss International Air Lines, Austrian Airlines, Eurowings, Lufthansa CityLine and Air Dolomiti, would not take part in the strike.
Lufthansa added that where possible, these airlines would "use larger planes on routes from and to Germany in order to bring as many rebooked Lufthansa passengers as possible to their destinations".
Lufthansa said the strike would be one of the biggest walkouts in its history.
It is the third strike to hit Frankfurt airport, Lufthansa's home base, in six weeks.
The airline's management is urging the pilots' union, Vereinigung Cockpit (VC), to restart negotiations as soon as possible.