Pilots “announce a strike at Ryanair,” the Cockpit union posted on Twitter.
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.
“From this moment on strike measures could happen at any time,” except during the Christmas period between December 23 and 26, the statement said.
Ryanair had a “last chance” to avoid strikes by immediately coming to the negotiating table, union president Ilja Schulz said.
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 airline could not immediately be reached for comment about the German strike plans.
With its more than 9,400 members in Germany, Cockpit was able to squeeze a pay, pensions and jobs deal out of mammoth carrier Lufthansa earlier this year, after repeated walkouts between 2014 and 2016 cost the group around 450 million euros ($530 million).