Ryanair has agreed to recognise the British Airline Pilots' Association (Balpa) to represent 600 UK-based pilots who account for 25% of Ryanair's pilots.
Although the airline had previously rejected the recognition of Balpa, it announced last month that it would change its stance towards unions and recognise the pilots society for the first time in its history to try an avert a strike in the run-up to Christmas.
On Tuesday the union and the airline company signed a voluntary trade union recognition agreement. The document states that Balpa will be recognised as the sole trade union representing the 600 Ryanair pilots based in the UK.
Brian Strutton, General Secretary of BALPA, said that the discussions to final the agreement were tough and have required compromise on both sides.
"Given Ryanair's previous hostility towards unions, today's agreement is an historic one. While we were initially sceptical about Ryanair's sincerity in offering recognition to us and other unions, our conversations and meetings with them have shown that they are genuine in wanting a constructive trade union relationship".
The union will have to open an election to choose five Ryanair Company Council representatives from the Balpa members employed by Ryanair. They will be in charge of negotiations on issues such as pay, hours and holidays on behalf of all the workforce.
Ryanair's chief people officer Eddie Wilson said that the company is keen on working alongside Balpa and that they have delivered pay rises of up to 20% to show their good faith and to prove they are serious about working constructively with unions.
"This rapid progress in the UK is in marked contrast to some other EU countries where we are still waiting for a response to our recognition proposals and where some unions have failed to put these substantial pay increases to our pilots."
"We now call on these unions to stop wasting time and act quickly to deliver 20% pay increases to our pilots in February, and conclude formal recognition agreements, which they are presently sitting on. Ryanair will not allow these unions to delay pay increases to our pilots."
Wilson has said that 35% of the company's pilots in Dublin still haven't received their pay increase and they have warned unions there to organise a vote among the pilots before January 31 or they will have to offer the pay increase to the pilots individually if they refuse.