Ryanair pilots who are members of the Irish Airline Pilots' Association (IALPA) are to go on strike on Wednesday December 20th.
Irish-based, directly-employed pilots - mostly captains - will withdraw their labour in an action that IMPACT says will either disrupt flights or "generate substantial costs" to the airline.
The pilots backed industrial action by a margin of 94% to 6% in secret ballots conducted over the last week.
The dispute is over what pilots say is Ryanair management's refusal to enter direct negotiations with the European Employee Representative Council (EERC) or IALPA as the sole independent representative body for pilots working in the company.
It says the airline has so far refused to recognise the EERC or IALPA - and insists that any discussion of pay and working conditions be conducted through management-controlled "employee representative councils."
The union has warned of further strike days if agreement is not reached.
Although the number of employees involved in the strike is fewer than the total number of Irish-based Ryanair pilots, the action will have an impact as planes cannot legally or safely fly without a captain.
IMPACT official Ashley Connolly says Ryanair is 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 union says it has made repeated attempts to open discussions with airline management in recent months.
In a statement, Ryanair said the threatened action is by less than 28% of its Dublin pilots - and the company noted it will deal with any disruptions to flights "if or when they arise".
The airline said: "While some disruption may occur, Ryanair believes this will largely be confined to a small group of pilots who are working their notice and will shortly leave Ryanair, so they don’t care how much upset they cause colleagues or customers.
"Ryanair has already confirmed that any Dublin pilots who participate in this industrial action will be in breach of the Dublin pilots base agreement and they will lose those agreed benefits which arise from dealing directly with Ryanair."
The company adds that it apologises "for any upset or worry" to customers caused as a result of the planned IALPA action.