The pilots' decision in Germany came after Ryanair held its first-ever negotiations with unions on Wednesday, which helped to avert planned pan-European industrial action by the airline's pilots.
The German pilots' association Vereinigung Cockpit said its negotiations with the company yesterday ended without results.
Ryanair has written to its German pilots this afternoon asking them to work as normal tomorrow to avoid disrupting the travel plans of thousands of German passengers during Christmas week.
"Ryanair will continue to engage with the VC union and its German pilots to try to agree a CLA in early January, so tomorrow's four-hour strike serves no objective other than to disrupt thousands of German passengers in Christmas week, exclusively so that the VC can impose a non-elected, non-Ryanair pilot (who is now suing the airline) on its Ryanair Pilots Council", the company said.More news: Fifth flu season death in San Diego region reported
Update 4.35pm: Ryanair is facing a four hour strike by pilots in Germany three days before Christmas.
The airline said it had tabled proposals on pay and conditions, procedures and dispute resolution for Irish-based pilots, and "looks forward to concluding an early agreement on these issues with its Irish Ryanair pilot company council".
Earlier on Thursday, Europe's largest discount carrier sent a letter confirming that the Impact union will now represent Irish pilots for collective bargaining, the labor group confirmed.
The union had last week called a strike of its Ryanair pilots in Ireland for December 20 but then the Dublin-based airline broke with its 33-year policy of refusing to engage with unions and the strike was called off. IMPACT says the ongoing progress means "the danger of industrial action had receded for the present".More news: Magic Leap introduces first product, Leap One
"This breakthrough, which was made possible by the principled resolve of Ryanair pilots, should be an encouragement to workers across the economy".
"It's just a short strike and we don't want to burden passengers too much ahead of Christmas", the VC's Schulz said.
The union's Assistant General Secretary Ashley Connolly said they would be reviewing Ryanair's status surrounding cabin crew, saying it would seem likely that management will recognise them.
"My colleagues are considering that correspondence, and we'll also obviously be talking to representatives of Ryanair pilots who were also involved in Tuesday evening's meeting".More news: Facebook says it wants your face data in the name of privacy
It said its threat of industrial action had diminished for the time being.