Strike action at Aer Lingus is set to go ahead next Monday 19 November, after SIPTU shop stewards refused to withdraw their notice of industrial action.
It had been hoped that the two-hour stoppage over pensions would be called off after a five-point plan to resolve the row was proposed by employers' body IBEC and ICTU.
However, SIPTU organiser Dermot O'Loughlin said that following a constructive and robust meeting, shop stewards were not in a position to withdraw the notice of industrial action.
He said the big issue was Aer Lingus' demand that any contributions to plug the deficit in the pension scheme must be offset by productivity from staff.
Mr O'Loughlin said those demands would have to be off the table for the strike to be called off.
He said that Aer Lingus was a company with €900m in cash, and that staff had already given enough productivity.
Mr O'Loughlin said SIPTU would be seeking clarifications on certain points from IBEC and ICTU - but that as of now, the strike is set to go ahead.
In a statement, Aer Lingus said it is regrettable that SIPTU has taken the decision "to use Aer Lingus customers as leverage in a dispute".
Aer Lingus said it is in the process of activating its disruptions plan, adding that it will do everything possible to minimise disruption to customers' travel plans on 19 November.
It said it will communicate with customers to inform them of any anticipated schedule changes.
The row over the €750m pension deficit at Aer Lingus and the Dublin Airport Authority has been hotting up for some months.
However, it had been hoped that the planned stoppage would be averted after IBEC and ICTU came up with a plan to get talks back on the rails.
The Dublin Airport Authority is not involved in the strike.