Talks are continuing between management at Aer Lingus and unions representing pilots at the Labour Relations Commission.
Both parties are hoping to avert industrial action at the airline, which is due to begin next Tuesday.
The dispute centres around a row over rostering.
Aer Lingus is warning that the outlook for the airline's passengers on Tuesday is looking increasingly serious with time to reach a deal running out.
The carrier said concerned customers can now alter their bookings online for free.