Talks between Aer Lingus management and unions on addressing the €750m deficit in the pension scheme have broken down.
SIPTU said industrial action is now the only remaining option for staff.
In a statement, Aer Lingus said the Labour Relations Commission had informed the airline that it was adjourning the discussions on the joint Aer Lingus/Dublin Airport Authority pension scheme indefinitely.
Aer Lingus said the discussions had been overshadowed and hampered by a union interpretation that a proposal targeting pensions worth 85% of final incomes had been agreed with the DAA.
The airline claimed that the DAA had confirmed directly to Aer Lingus that the proposal under discussions with unions did not target any such pension coverage level.
The airline called on the DAA and unions to resume discussions and clarify their positions.
Up to now Aer Lingus has refused to consider any solutions targetting more than 66% of final salary - but said it remained available to resume discussions.
SIPTU Sector Organiser Dermot O'Loughlin said the LRC Chief Executive had confirmed the pension talks could go no further as the gap between the sides was unbridgeable.
He said Aer Lingus had refused to go to the Labour Court, so all avenues of dispute resolution were now exhausted - and industrial action was the only option left to staff.
He said the union's industrial action committee will meet tomorrow to decide on the timing and form any action.
SIPTU added that talks are continuing with the Dublin Airport Authority and that there is no threat of industrial action at the DAA at this time.
