Air Berlin has been forced to cancel about 100 flights after an “exceptionally high” number of its pilots called in sick.
The airline, which filed for insolvency last month and is only still operating because of a German government bridging loan, said Tuesday’s apparent strike threatened its existence and hurt its chances of saving jobs.
The pilots’ union, Vereinigung Cockpit, said it had not called the action – adding it was surprised that 200 pilots had failed to report for duty.
Air Berlin, which is Germany’s second-largest carrier, said most of those off work were plane captains.
It has been in financial trouble for years, and industrial relations are at breaking point.
In an internal memo to staff, seen by the Reuters news agency, chief operations officer Oliver Iffert wrote: “No company could possibly be seen in a worse light than Air Berlin today.
“We must return to stable operations. That is crucial in order to bring talks with investors to a successful conclusion.”
Air Berlin filed for insolvency after a major shareholder, Abu Dhabi-based carrier Etihad, refused to extend its cash lifeline.
The subsequent €150m (£135m) loan from the authorities allows Air Berlin to continue flying for three months as rivals circle above – hunting an opportunity to capitalise ahead of a Friday deadline for bids.
Ryanair is expected to be in the mix.
It has accused the German government of wanting the country’s biggest carrier, Lufthansa, to take control of Air Berlin’s viable operations.
German media has reported Lufthansa wants to take up to half its 140 planes and 3,000 crew for its Eurowings budget airline.
Eurowings currently leases 38 aircraft from Air Berlin – and because of this, it too has had to cancel flights because of the pilots’ walkout.