Aer Lingus has told unions it is axing 87 cabin crew jobs at Shannon because the staff refused to fly new transatlantic routes using smaller planes with lower staffing levels.
It is understood staff will be offered the options of redeployment to Dublin or Cork, voluntary severance, or possibly redundancy.
However, a spokesman declined to confirm whether there would be compulsory redundancies.
Staff may also be offered the option of leave of absence to work for ASL Aviation/Air Contractors Ltd, the company from which Aer Lingus is leasing the planes for the new transatlantic services.
Last July, Aer Lingus announced it was increasing its transatlantic services from Shannon and was leasing planes from ASL Aviation/Air Contractors Limited.
Serving Aer Lingus pilots agreed to fly the new smaller planes, but the cabin crew union IMPACT said it would not operate the flights with the four-member staff complement sought by the company.
Aer Lingus warned unions in recent weeks that if they did not accept the new staffing levels, they would instruct ACL to recruit the staff themselves and operate the services, which commence in January.
The company had said that if the new staffing levels were accepted, they would create 40 jobs.
IMPACT has condemned the move and described it as an act of "wanton destruction" on the livelihoods of loyal workers.
The union said its members will fight the decision and said the action of Aer Lingus management was entirely unnecessary.
It said cabin crew are balloting for industrial action, with the ballot due to be completed on 30 October.
In a memo to staff, Aer Lingus Chief Executive Christoph Mueller said that it was not a commercially viable option to retain a single short-haul crew base in Shannon.
He stressed that there would be no reduction to the Shannon schedule or fleet, but that the resultant job creation would not be happening within Aer Lingus, but within ACL.
He said this was a situation the company had never contemplated being in.
Mr Mueller said that what started out as a great opportunity to protect existing jobs for Aer Lingus crew, to create 40 extra jobs, and to provide promotional opportunity has ended up making the Shannon cabin crew base unviable.
Airline sources also stressed that the expansion in their services from Shannon would still benefit the Shannon area, but any resultant job creation would now happen outside of Aer Lingus rather than within the company.
The company is now entering a 30-day consultation period with unions.
IMPACT official Michael Landers accused management of attempting to bully its own staff into submission with an ultimatum and then slamming the door on discussions when it announced it would outsource crew.
He said cabin crew representatives had made it clear they were willing to discuss the matter further, and had not, contrary to claims by management, refused to crew the flights with a complement of four crew members.
Pilots' union IALPA, which has agreed to fly the new routes, said it was monitoring developments at Shannon and urged management to return to talks with cabin crew.