Ryanair could face up to 20m euros (£18m) in compensation claims after cancelling thousands of flights due to a shortage of pilots, it has warned, reported BBC.
The budget airline plans to cancel 40-50 flights every day for the next six weeks, after it admitted it had "messed up" the planning of pilot holidays.
An internal memo seen by the BBC suggests the pilot shortage could continue until the end of the year.
There is no suggestion this means the disruption will extend beyond October.
In a letter to pilots, chief operations officer Michael Hickey said the firm's crewing forecast to the end of December was "for tighter pilot numbers".
The letter shows Ryanair pilots were only informed on 13 September of the staff shortage facing the company yet Mr Hickey outlined that it knew last year they may face a leave backlog.
Pilots have been asked to work during their booked holiday to cover the gaps and their rota pattern is also likely to be disrupted.
In the letter, Mr Hickey said these pilots would be "helping protect the integrity of the operation during the remainder of the flight year".