A German pilots' union has told its members that industrial action against Irish carrier Ryanair is likely to be needed to force management to overhaul the way it negotiates with its staff.
Ryanair does not recognise trade unions and negotiates with pilots via an internal collective bargaining system it says is recognised by Irish law.
Pilot unions say the current system does not allow for genuine negotiations and should be replaced with a pan-European system that allows them to properly represent pilots.
The Vereinigung Cockpit union says more than half of the Ryanair pilots working from bases in Germany are members.
It said in a memo to pilots that it hoped it would not be necessary to hold strike action but "realistically it probably will be, first to begin negotiations and later if the negotiation stalls".
Asked about the memo, Ryanair said in a statement that "these German union claims are without foundation".
"Ryanair and its pilots are continuing to use its collective bargaining procedures while German pilot unions waste their time issuing press releases," it added.
Ryanair, whose chief executive is Michael O'Leary, says it offers better pay and conditions than rivals.
The union has set up a company council made up of Ryanair pilots and one lawyer, which it said was a necessary step before a strike can legally be called.
It said it has asked Ryanair to start talks with the union on a new labour agreement and that Ryanair refused.
A pan-European pilots group, the European Employee Representative Council (EERC), has been set up in recent months by Ryanair pilots. It said in a statement on its website that industrial action "may be necessary".
The EERC group was formed after Ryanair announced the cancellation of about 20,000 flights in September due to a shortage of standby pilots.