Aer Lingus has told unions it is cutting 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".
A spokesman declined to confirm whether this could include 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.
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.
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.
Some weeks ago, Aer Lingus warned unions 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.
Aer Lingus had said that if the new staffing levels were accepted, they would be creating 40 new jobs.
In a memo to staff, Chief Executive Christoph Mueller said that it not a commercially viable option to retain a single short haul crew base in Shannon.