Ryanair pilots who are members of the Irish Airline Pilots' Association (IALPA) are to go on strike next week.
Directly-employed pilots will stop work for 48 hours from midnight on Thursday August 22nd.
Their union served strike notice on the company on Wednesday evening - and said Ryanair pilots would notify the company of further strike days "in due course."
The move comes after 94% of them voted to back industrial action in a dispute over pay and working conditions.
The union said it had submitted a 30-page proposal to Ryanair management in March this year, which sought pay levels and structures it says are in line with sector norms.
The IALPA claim also included proposals on pensions, working conditions and related matters.
On Tuesday, both sides accepted an invitation from mediator Kieran Mulvey to attend talks.
But the union said "a substantive counter-proposal from Ryanair management" was not made at the mediation meeting.
Fórsa national secretary Angela Kirk said Ryanair pilots told her they had been "forced into industrial action by the company's failure" to offer any significant response to their proposals over a four-month period.
Some 180 directly-employed Ryanair pilots based in Ireland, who are members of IALPA, were eligible to vote in the strike ballot.
Ryanair pilots who are employed by agencies, or have so-called 'self-employed' status, cannot be balloted under Irish employment law.
While Ryanair said the pilots withdrew from the mediation talks "when no progress was made on their unrealistic and unimplementable pay proposals."
The company claimed pilots are seeking pay increases of 101%, on top of current annual pay of over €172,000.
"Pilots are insisting on these pay demands being met, just one day after Norwegian announced the closure of its Dublin operations with the loss of over 120 crew jobs, despite the fact that Ryanair has a surplus of over 500 pilots due to the delayed delivery of over 30 MAX aircraft this winter, and just 10 weeks before a 'no-deal' Brexit could cause further disruption to air travel and airline jobs in Ireland and the UK", the company added.
Ryanair's chief people officer Eddie Wilson said: "We have done everything in our power to avoid disruption to our flights and our customers' holidays.
"However, no company can concede to grossly unreasonable demands from its highest paid workers for a further pay increase of over 100% (when they already agreed and received a 20% pay increase earlier this year) at a time when the airline industry is in crisis."