Strike action at embattled Ryanair intensified Tuesday, with German pilots the latest to plan possible walkouts over conditions, following similar moves by staff based around Europe.
Germany's powerful pilots' union said members would strike at Ryanair for better pay and conditions, although they insisted they would not disrupt flights over the Christmas holiday.
They aim "to force the start of talks to create employment and pay conditions for Ryanair pilots in line with the market", the union said in a statement.
Ryanair had a "last chance" to avoid strikes by immediately coming to the negotiating table, union president Ilja Schulz said.
The Irish airline, which is cancelling thousands of flights because of pilot shortages, said it had not been notified of any industrial action by its German pilots.
Unions have long complained that no-frills Ryanair does not offer pilots pay and conditions up to standards elsewhere in the aviation industry.
German prosecutors searched offices belonging to the carrier at six airports last year, part of an investigation into possible tax evasion and withholding salaries against two British temp agencies that supply the Irish airline with self-employed pilots.
In its statement, Cockpit claimed pilots were leaving the airline "in droves" for the better conditions offered by other carriers, leaving Ryanair with a shortage of aircrew.
Italian pilots for the Irish carrier have already set dates for strike action, while Irish and Portuguese aviators have announced unspecified industrial action.
Ryanair said last week that it would "ignore" the Italian pilots' move, saying its staff rarely heeded calls to walk out.
The carrier on Monday said some of its pilots in Dublin had voted for strike action.
The unspecified industrial action was backed by less than 28 percent of around 300 pilots based in the Irish capital for Ryanair, the airline said.
Although the airline has around 300 pilots based in Dublin, reports said the strike ballot was issued to the 84 pilots directly employed by Ryanair.
The move comes less than a week after Ryanair pilots and flight attendants in Italy announced a four-hour strike for December 15.
The planned industrial action comes after Ryanair said in September that it had to cancel 20,000 flights until March because of pilot scheduling problems.
Air traffic control delays and weather disruption also contributed to the cancellations.
Despite such difficulties, Ryanair said last month it still expected to deliver annual profit after tax of 1.40-1.45 billion euros ($1.65-1.71 billion).