SIPTU members at the Dublin Airport Authority have rejected company proposals dealing with new pay structures, flexible work practices and dispute resolution mechanisms.
The vote was 68% against, with 32% in favour.
However, employees belonging to Mandate voted 83% in favour, with 86% of those belonging to IMPACT backing the proposals.
Craft workers and airport police and fire personnel are engaged in separate talks that have not yet concluded.
The proposals would have seen pay rises of between 3 and 4% per annum over the next three years – with the higher increases reserved for staff earning below €41,600.
In return, staff would have had to agree to significant changes and flexibility, including "interoperability" between terminals one and two in Dublin Airport, which currently operate with separate workforces.
There would also have been new employee engagement structures, culminating in a binding Internal Resolution Council.
SIPTU Organiser Neil McGowan said union representatives will now consult with workplace representatives and the wider membership to decide on the next steps in progressing their claim for improved terms and conditions of employment.
Following the rejection, DAA Group Head of Employee Relations John McCormack told staff he was disappointed that the proposals had not been accepted, and which are now withdrawn.
He acknowledged that many employees had significant concerns about some elements of the proposals, and said the company would now take some time to consider the issues raised.
