Union leaders were last night considering a new initiative aimed at averting industrial action over the planned break-up of Aer Rianta.
They are now likely to seek renewed talks with the Minister for Transport, Mr Brennan, who yesterday offered new assurances about the future of Aer Rianta staff.
The Minister wrote two letters yesterday to the general secretary of the Irish Congress of Trade Unions, Mr David Begg, seeking to defuse unions' anxiety over his plans for CIÉ and Aer Rianta.
One letter followed a demand by the president of SIPTU, Mr Jack O'Connor, hand-delivered to the Department of Transport yesterday morning, that Mr Brennan clarify his position on CIÉ "within minutes".
Mr Brennan replied shortly afterwards with a letter to Mr Begg restating his commitment to resolving the impasse over CIÉ through discussion with unions.
Mr O'Connor's unusual demand followed a newspaper report yesterday suggesting that Mr Brennan remained committed to his privatisation plans for the Dublin bus market. His swift reply defused a potential crisis and meant a planned meeting with unions next week on CIÉ can go ahead.
In a second letter to Mr Begg, the Minister said he wished to state clearly his "commitment to preserving the terms and conditions of Aer Rianta workers".
Legislation effecting the break-up the company, he added, would ensure that lesser terms and conditions than those already existing could not be imposed on the workers.
Mr Brennan also promised to make the financial information, on which the decision to break up the company was based, available to the unions in advance of any legislation.
This was seen by union officials yesterday as a highly significant development, in light of their continual requests for the Minister to furnish a business plan on the airports' future.
Members of SIPTU, however, were unaware of Mr Brennan's letter when they held general meetings at Dublin and Shannon airports at lunchtime.
At the Dublin meeting, workers decided that industrial action at the airports should be resumed within two weeks. Particular anger was expressed at the failure of Department of Transport officials to provide satisfactory guarantees on workers' future pay and conditions, in talks with the unions on Wednesday.
To the surprise of other Aer Rianta unions, SIPTU representatives then withdrew from a group of unions meeting scheduled for yesterday afternoon at the office of the Irish Congress of Trade Unions.
Mr Michael Halpenny, national industrial secretary with SIPTU, said the decision not to attend was for "logistical reasons".
He described the vote for industrial action as a "decision in principle" and said the intention was to minimise disruption to the travelling public and target instead Ireland's Presidency of the EU. SIPTU would attend a group of unions meeting next week, to co-ordinate plans.
It is considered unlikely, however, that SIPTU would engage in industrial action at a time when other unions are pursuing a significant intervention by the Minister.
Mr Arthur Hall of the TEEU said Mr Brennan's letter to Mr Begg amounted to a "180-degree turn" from his previous position.
Unions now needed to sit down with the Minister to hear how he planned to implement the commitments he had given.
"We have to give him that opportunity, although I would stress that it is his last opportunity," said Mr Hall.
"If he cannot back up his commitments with action, then industrial action will be inevitable."
