Impact, which represents Irish-based pilots, has agreed to meet the low-priced carrier's management on Tuesday evening ahead of the planned strike on Wednesday.
Impact, the Irish pilots' union, said it had received Ryanair's letter on Friday morning.
The union asked management to release its Ryanair pilot representatives to prepare for and attend the meeting.
On Friday, Ryanair agreed to recognise unions for the first time ever, but unions wanted talks to ensure the details of the agreement.
According to the German pilots' union, Ryanair offers no continued payment of wages in the event of sickness, no obligatory work schedule, no retirement planning and a widely prevalent system of pseudo-self-employed pilots.
Confirmation that the meeting with Impact will now take place Tuesday in advance of the Wednesday deadline was confirmed by Ryanair on Saturday.
The Irish union responded on Sunday that it would be "happy to do that".
A spokesman added: "Once we meet, we can take a decision on deferring industrial action".
The Impact trade union is looking for further reassurances from the airline before calling off its planned walkout on Wednesday.
Ryanair has never recognised unions, but it said it would change this policy in order to avoid disruption to flights and passengers in Christmas week.
In October, Mr O'Leary wrote to his airline's pilots to offer them better pay and conditions after Ryanair was forced to cancel thousands of flights.