A strike by cabin crew at Lufthansa was due to start this morning at the carrier’s Frankfurt airport hub.
The eight hour walk out over pay and conditions is expected to lead to disruption to passengers throughout the day.
The airline is to prioritise long-haul flights and "wherever possible" these would not be cancelled.
But the industrial action "may lead to unscheduled flight delays and cancellations".
And there was uncertainty over the precise impact the strike would have on services.
Lufthansa has about 19,000 cabin crew and the UFO union, which is in dispute with the carrier, represents about two-thirds of them.
The union warned that strikes could cause disruption to hundreds of flights.