Air Berlin cancelled nearly every twentieth flight on Wednesday, or 32 out of a total of 696 flights. Tuifly said that it had also cancelled 24 flights, down from 99 planned for Wednesday to 75.
The reason for the cancellations was that Tuifly, which also provides staff and airplanes to Air Berlin, said it was experiencing crew shortages.
A large number of Tuifly staff called in sick, most likely because they are concerned about their jobs as Air Berlin and Tuifly have been in discussions about a partial merger, according to Spiegel.
“Tuifly regrets the inconvenience that this has caused for passengers,” the company wrote in a statement.
“The massive, short-notice calls for sick leave by cabin and cockpit staff has hurt customers and other employees greatly. Right now during the autumn holidays, it has affected many families with children.”
Over Monday and Tuesday, 30 percent of Tuifly flights had been delayed because of the staff shortages.
Air Berlin confirmed on Wednesday that it would discuss transferring part of its fleet to a new group founded by package tour giant Tui and Gulf carrier Etihad.
Air Berlin could bring 35 of its aircraft, including 14 already leased from Tuifly, into a "new airline group to be founded by the Tui group and Etihad", it said in a statement.
Tuifly tried to quell staff concerns about the plans by saying in a statement on Wednesday that “existing labour agreements will remain intact” and that the company did not plan to move its base from Hanover.
The plans with Air Berlin remain subject to negotiation and regulatory approval, the statement continued.
In a separate statement, Etihad said "the new airline group would serve a comprehensive route network from Germany, Austria and Switzerland".
Air Berlin shareholder Etihad has kept the struggling airline alive with regular cash injections in recent years.