SIPTU President Jack O'Connor has authorised the serving of notice of industrial action on the Dublin Airport Authority in a row over pensions.
The union said it will stage industrial action on Monday 1 October if the dispute is not resolved in the meantime.
Labour Relations Commission Chief Executive Kieran Mulvey confirmed that talks aimed at resolving the dispute over the €700m deficit in the Irish Aviation Pension Scheme for the two companies had been adjourned.
Mr Mulvey said this was to allow the LRC to try to formulate a proposal that might have a reasonable prospect of resolving the row over the next number of days.
He said when that task was completed, the commission will recall the parties.
SIPTU said the action will take the form of two staggered two-hour work stoppages on a location-by-location basis.
Mr O'Connor stressed that this was a unique situation where the row was not the fault of Aer Lingus, the DAA or the unions, but that the blame lay with the Pensions Regulator.
He blamed the dispute on tough new funding regulations for pensions, which he said would have the ridiculous and absurd effect of forcing schemes to close instead of protecting them.
Mr O'Connor forecast that the pensions funding standard issue would lead to many strikes over the next three to six months, as up to 310,000 workers would have to battle to preserve their pension entitlements.
The DAA said it was "very disappointed" to have been served the notice.
A spokesman added: "To serve notice of industrial action at this time, while the LRC process is ongoing, is totally unwarranted and will cause unnecessary concern and inconvenience to the travelling public."
Sources have described the issues involving the IASS pension scheme as particularly complex, partly because Aer Lingus is now a private sector company, while the DAA is a State agency.
In addition, the IASS has a residual liability for pensions for workers at aircraft maintenance firm SR Technics, which closed some years ago with the loss of over 1,100 jobs.