"As a pilot group we regret that you are not willing to solve the problems Ryanair is facing now", the letter reads. The bonus payments are also conditional to pilots working over 800 flight hours in the year ending October 2018.
He added: "We have some goodies to discuss, but if pilots misbehave, that would be the end of the discussion".
Citing pilot sources, Irish national broadcaster RTE said late on Thursday pilots from 55 bases had rejected the bonus pay offer, including at large Ryanair hubs in Dublin and London's Stansted airport.
"The low cost airlines are arguably more vulnerable to a pilot shortage because of their growth, which is now compounded by their size", said Gerald Khoo, an analyst with Liberum.
Ryanair has offered pilots a €10,000 pay rise to stave off competition from other carriers after a week of flight cancellations and customer dissatisfaction but the company told staff that they could "kiss goodbye" to better pay and conditions if they took industrial action.
Mr O'Leary blamed the crisis on the mismanagement of pilots' holidays.
But two pilots familiar with efforts to negotiate with Ryanair said the company has ignored the ultimatum, allowing the deadline to pass.
Michael O'Leary insisted there is no problem between the airline and its pilots. They will get it back in January.
Suu Kyi finally breaks silence on Rakhine state turmoil, invites global scrutiny
The Rohingya community who fled from Myanmar in the end of Aug has become a matter of concern for everyone. On Aug. 25, a Rohingya militant group staged a series of attacks against police outposts in Rakhine state.
O'Leary said the decision was taken to cancel what amounted to 2% of the airline's total flights to avoid a sharp increase in delays because of a lack of reserve pilots.
Ryanair's crisis was due in part to a change in Irish labor laws that forced the airline to compress a year's worth of vacation into a nine-month transitional period, according to Bloomberg.
He accused some pilots of being "precious about themselves" and "full of their own self importance".
"I would challenge any pilot to explain how this is a hard job or how it is they are overworked, or how anybody who by law can't fly more than 18 hours a week could possibly be suffering from fatigue".
Ryanair has updated customers about the flight ordeal, which will affect 315,000 people.
"Michael O'Leary's statements are disgusting, we regularly fly over 40-44 hours in a week, 50-60 duty hours, waking up at 4 am plus commuting long distances".
Some 315,000 Ryanair customers are expected to be affected by the cancellations over the next six weeks, but the airline's investors have had a pretty smooth ride-the airline's share price rose on Friday, almost back to where it was before the scheduling snafu emerged.
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