The one-day industrial action will take place on Wednesday December 20 and will mostly involve captains.
Trade union Impact said it would either disrupt flights or generate substantial costs for the airline.
Pilots from the Irish Airline Pilots' Association backed the industrial action overwhelmingly during secret ballots.
The dispute is about winning independent representation for pilots in the company, Impact said.
Although the number of employees involved in the strike is fewer than the total number of Irish-based Ryanair pilots, the action will have impact because planes cannot legally or safely fly without a captain, the union added.
Impact official Ashley Connolly said Ryanair was the only Irish-based airline that refuses to recognise independent pilot representatives.
"This dispute is solely about winning independent representation for pilots in the company.
"Management's failed negotiating model has let down shareholders and tens of thousands of passengers, whose flights were cancelled this year because company-controlled industrial relations proved incapable of recruiting and retaining enough pilots.
"The failed policy threatens to further disappoint shareholders and passengers, and further damage the airline's reputation, because experienced pilots continue to leave the airline in droves.
"This dispute is about securing a safe space for negotiations, with independent representation that pilots can have confidence in."