German pilots are expected to announce strike action against Ryanair today - adding to the airline's industrial relations woes.
Janis Georg Schmitt, of the Vereinigung Cockpit union, said it was expecting a "big vote for yes" following a ballot for industrial action over pay.
Mr Schmitt said members were demanding that a "fixed" portion of their income be increased and a flexible portion - that depends on the number of hours they fly - be reduced.
"We do expect a big vote for yes," he said. "I don't think there will be industrial action directly after the vote, but possibly a week later."
Irish-based pilots directly employed by Ryanair have already held three 24-hour stoppages.
Some 3,500 passengers will be hit by flight cancellations during a fourth strike by the Irish-based pilots this Friday.
Ryanair said this represented 20 out of 300 flights that are scheduled on the day.
The directly employed staff, who represent a quarter of the pilot workforce, want their length of service to determine who gets holidays at popular times of the year, base transfers and promotions.
Six hundred flights were cancelled last week when cabin crew in four countries went on strike.
Meanwhile, the airline has denied it was trying to intimidate staff by putting 100 pilots and 200 cabin crew on protective notice last week.
In a letter to Ryanair's chief people officer Eddie Wilson, the Spanish Sepla union accused the airline of trying to intimidate its staff after the Irish strikes.
It warned the budget carrier it could find that "this unrest is only the beginning".
The letter followed the airline's decision to put more than 300 staff on protective notice of lay-offs this October as it moves aircraft from Dublin to Poland.
Ryanair said this was a "commercial move".
"The actions you have taken after strikes by our colleagues in Ireland seem to have an intimidating purpose… The memo giving information, which is only applicable to employees in Ireland, has been sent to every single Ryanair pilot," Sepla said.
It warned that the airline's actions had in fact had the opposite effect.
A Ryanair spokesperson said that claims of intimidation were nonsense.