A German cabin crew union on Friday called a three-day strike at Lufthansa subsidiary Germanwings, plunging passengers into turmoil over the busy end-of-year holiday as it ramps up a bitter row over pay and conditions.

The UFO union said Germanwings employees would strike from 2300 GMT on Sunday until 2300 GMT on Wednesday as talks with bosses remain deadlocked.

The strike period covers New Year's Eve and the January 1 public holiday.

"We are deliberately announcing the strike early so Germanwings passengers have a chance to book flights with other airlines or make alternative travel plans," said UFO vice-chairman Daniel Flohr in a video message.

The union stopped short of announcing a fresh stoppage at flagship carrier Lufthansa itself, but warned that more strike calls could follow from January 2.

Flohr said UFO took stoppages at this time of year -- when many people are travelling to meet friends and family -- "very seriously".

But Germanwings management had "given its employees no clear options for the future," he argued.

A Lufthansa spokesman had earlier condemned the union's latest strike threats, saying "this is no way to resolve the conflict".

Board member Detlef Kayser said in a statement that "UFO has refused for weeks to put concrete demands in writing."

A strike by cabin crew will likely keep many Germanwings planes on the ground over the New Year holiday
A strike by cabin crew will likely keep many Germanwings planes on the ground over the New Year holiday AFP / INA FASSBENDER

Lufthansa and UFO have for months been locked in an increasingly bitter dispute that has triggered repeated walkouts.

A 48-hour stoppage at the main Lufthansa brand led to 1,500 cancellations at German airports in November, affecting 200,000 passengers.

A one-day warning strike in October prompted several dozen flight cancellations at Lufthansa subsidiaries Eurowings, Germanwings, SunExpress and Lufthansa CityLine.

As well as demanding higher wages, especially for entry-level jobs, the UFO union is seeking better benefits and easier routes into long-term contracts.

Lufthansa for a long time refused to discuss the demands, claiming the union no longer had the right to represent its 22,000 cabin crew employees owing to an internal leadership struggle.

The company even challenged UFO's legal status in court.

But the group changed its stance during November's massive strike, agreeing to arbitration with UFO leaders and two mediators.

The UFO union on Sunday said those talks "had failed".

Both sides have agreed to keep details of the talks confidential but German media reported they could not even agree on which topics should be covered by the arbitration.

Aside from pushing its demands for better pay, UFO is reportedly also seeking assurances that certain staff members will not face disciplinary action over the strikes.

Lufthansa said it was putting its hopes in a fresh round of talks proposed by the mediators for January, but UFO denied a new date had been agreed.