SIPTU has rejected the Dublin Airport Authority's latest proposal aimed at resolving the company's pension dispute.
SIPTU is in negotiations with the DAA and Aer Lingus over how to resolve an estimated €748m hole in the combined pension scheme, which is known as the Irish Aviation Superannuation Scheme (IASS).
According to the union, the proposals on the table from the DAA at the moment would provide workers with at most 50pc of their salary.
While the basic numbers of the DAA proposal is broadly more generous than what Aer Lingus is offering, it is not enough, says SIPTU.
The union posted a circular to workers yesterday highlighting the discrepancy between what staff could expect if no changes were made and if the proposals were accepted.
A person with a pensionable salary of €36,000 and five years from retirement would have a pension of €34,500 under the current scheme, but that would fall to €29,775 under the DAA plan.
SIPTU sector organiser Dermot O'Loughlin, however, warned the "pensionable salary" was in most cases much lower than what the worker actually took home.
"About 80pc of staff are doing shift work, and with that comes various allowances for working nights and unsociable hours, so the pensionable salary would generally be only a portion of what the worker has been earning throughout their career."
In a letter to the DAA yesterday, SIPTU said there were two "areas of contention" over what was apparently on the table from the DAA.
The financial proposals were "inadequate", the union said, while SIPTU also objected to the introduction of medical assessments as part of resolving the issue.
The union maintained the dispute was a purely financial one and so the assessments shouldn't be part of any deal.
A spokesman for the DAA, however, said it had "not made any formal offer to trade unions in the ongoing pensions talks".
"Contact between DAA and staff representatives is continuing in relation to this matter and a number of issues remain to be resolved. DAA has no further comment to make at this time," the spokesman added.
The latest move on the DAA side of the pension comes only days after SIPTU called off a strike among its Aer Lingus staff over the dispute.
Aer Lingus wants to freeze pay at the airline for four years in return for a one-off payment into the scheme. It also wants to freeze contributions to the defined benefit plan.