Ryanair pilots in Germany plan to strike for 24 hours from Friday, their union said on Wednesday, adding to action already planned in Ireland, Sweden and Belgium.
Ryanair late last year said it would recognise unions, but has so far not agreed any collective labour deals with staff across Europe.
Ryanair has already cancelled 6 percent of the more than 2,400 flights it has scheduled across Europe on Friday as a result of the strikes planned in the other three countries.
The walkout by pilots based in Germany will start at 0101 GMT on Friday, affecting all flights from Germany, Vereinigung Cockpit (VC) said in a statement.
The VC union said last month that talks with management had ended without the progress they hoped for and they gave Ryanair until Monday to put forward a new offer.
The union is demanding improved pay and conditions for Ryanair pilots, but said on Wednesday that Ryanair had ruled out any increase in staff costs.
"Improvements are not possible without an increase in staff costs in the cockpit," VC President Martin Locher said. "At the same time, Ryanair has not yet said where there might be room for manoeuvre."
Ryanair executives are due to hold a news conference in Frankfurt later on Wednesday.
Ryanair has further angered unions by threatening to shift jobs if walk-outs hurt its business.
In the row with Irish pilots, Ryanair has proposed that a third-party mediator join talks.
Dutch pilots' union VNV is also considering calling for strikes on Friday but has not yet taken a decision, a spokesman said.
