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 company said it would only negotiate with pilots who worked for the company and VC officials and so the talks were halted.
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.
Vereinigung Cockpit (VC), a German pilot trade union which represents a number of Ryanair pilots in the country, said the "warning strike" will affect all flights operated out of German airports during that four-hour period.
IMPACT has accepted an invitation from Ryanair management to meet on 3 January "to agree a comprehensive recognition agreement that will establish collective bargaining procedures in the airline".
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Ryanair met with pilots and union reps on Tuesday in a massive U-turn on its long-standing policy.
Ryanair has written to pilots saying it will contact their trade union today about formal union recognition.
"It's just a short strike and we don't want to burden passengers too much ahead of Christmas", the VC's Schulz said.
Last week, Ryanair was facing a threat of strikes from multiple groups of its pilots across Europe.
Ryanair said the strike is "unjustified" given that the sides have agreed to meet again on January 5, adding that the pilot council which attended the talks had not been elected by its own staff and contained one person who is now in litigation with the company.
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Ryanair said separately that it had formally recognized Impact while also submitting proposals on issues including pay and dispute resolution.
Commenting on the official recognition of the union by Ryanair, IMPACT official Ashley Connolly described it as a "historic achievement" that would resonate beyond the company.
The move eased tensions but unions warned that strikes remained an option if the Dublin-based carrier was not serious about the discussions.
"We will be engaging with Ryanair company council, which is made up of our Ryanair pilots, and we will be developing our agenda", she told RTÉ's News at One.
"Rather, Ryanair is trying to win time and attempting to delay the beginning of collective bargaining", Schumacher said.
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