Union leaders are on standby to receive a letter from the Taoiseach over the weekend that could decide the future of social partnership.
Mr Ahern is expected to confirm that the Government will support measures to maintain employment standards in any talks on a new national deal.
It is anticipated he will outline the Government's position in a letter to Irish Congress of Trade Unions general secretary David Begg, to be delivered either today or early tomorrow.
The development follows a series of high-level meetings between union and Government representatives this week. But it was still not known last night if Mr Ahern's commitments would be strong enough to convince Siptu to continue its support for the partnership process.
The union's national executive council meets tomorrow afternoon to consider the position, ahead of a special delegate conference on Monday.
That conference will decide how Siptu's 77 delegates vote at an Ictu conference on Tuesday, called to discuss whether unions should enter talks on a new deal.
A total of 400 delegates will be entitled to vote at the Ictu meeting. If Siptu's delegation votes not to enter talks, there is unlikely to be enough support from other unions to enable negotiations on a successor to Sustaining Progress.
Siptu's reluctance to remain in partnership arises from the dispute over Irish Ferries' plans to replace unionised seafarers with cheaper labour from eastern Europe.
Talks on that issue are continuing, but in the meantime it wants commitments from the Government on measures to prevent a "race to the bottom" in employment standards.
Separate meetings about the issue were held this week between union leaders and Mr Ahern, Minister for Enterprise Micheál Martin and the secretary general of the Department of the Taoiseach, Dermot McCarthy.
It is considered unlikely that any letter from the Taoiseach will include specific promises on legislative changes to underpin employment standards.
Sufficiently strong general commitments could be enough to persuade Siptu to enter talks with a view to negotiating detailed arrangements at that stage.
Siptu is not the only private-sector union hardening its position before new talks.
At a meeting this week Ictu's private-sector committee drew up what it described as a "limited agenda" of minimum demands that unions will take into any talks on a successor to Sustaining Progress.
On pay, private-sector unions will seek a local bargaining clause which would allow workers in highly profitable enterprises to pursue "top-up" pay increases.
There is deep frustration among some unions that, while employers can plead inability to pay the terms of a national deal, unions are prevented from pursuing higher-than-normal increases in firms that can afford them.
Childcare, pensions and work permits are also among the items on the private-sector unions' agenda.
They claim, for example, that new work-permits legislation proposed by the Government falls short of what was promised and seeks to continue a system of "bonded labour", which restricts the right of work-permit holders to change jobs.
Management at Irish Ferries and Siptu met at the Labour Relations Commission on Thursday, but it is understood no progress was made towards resolving their dispute.
The matter is to be referred back to the Labour Court by the end of the month if no agreement has been reached.
