Siptu shop stewards are meeting today to discuss the rejection of the Aer Lingus cost-saving plan.
Aer Lingus is seeking to introduce more flexible work practices for some 1,800 staff, who mainly work in ground operations that it says will save the airline about €10 million a year.
A deal on new work practices by Siptu members at the airline was agreed by management and union negotiators in February.
However, the proposed deal was rejected by a three-to-one majority of workers in a ballot, results of which were released on Monday. In some sections of the airline, particularly in Shannon airport, Siptu members voted almost unanimously against the deal.
Siptu claimed the company's failure to produce workable rosters in line with the proposals was a major factor in the rejection.
The proposed deal averted a possible strike in February that could have affected up to 20,000 passengers per day.