It's set to be a huge week in the history of industrial relations in Ireland. Some time over the next few days, Kieran Mulvey, the facilitator of the Croke Park deal between unions and the government, and the chief executive of the Labour Relations Commission, will outline a clarification of what was agreed between both sides in March. Then on Wednesday, the powerful public service committee of Ictu will meet to decide whether to recommend the deal. Its decision could well determine whether the rest of the year will be relatively peaceful or pockmarked by serious industrial action.

Last night, Siptu leader Jack O'Connor made an impassioned defence of the Croke Park pay deal, urging members to back the government's offer as the "only survival strategy" in the current climate.

Speaking in Athy at a celebration for May Day, O'Connor said that public servants should not regard a vote in favour of the deal as backing the government. "The proposals guarantee jobs, preclude compulsory redundancies, minimise outsourcing, prevent further pay cuts and provide a framework for restoring lost pay over time," he said.

O'Connor and other union leaders, who are backing the deal in the face of massive opposition from ordinary union members, will need Mulvey's clarification to be a convincing one.

The Sunday Tribune understands that it will provide a bit more certainty on pay for the unions as well as some further detail on pensions, outsourcing and a revision of the teachers' contracts.

But informed sources have pointed out that it is impossible to secure certainty in such uncertain times.

It is understood there is a growing opinion within government that it would better suit its budgetary strategy if the deal was rejected. The belief is based on the fact that rejection would leave the government on the 'high moral ground' in that it would have offered the 'deal of the century' to public servants, who would now have only themselves to blame for rejecting it.

This would allow finance minister Brian Lenihan to proceed with public backing to extract more pay cuts next December. Such a move would be a far easier way of achieving the required €3bn savings than lengthy union reforms which would probably never yield the same level of savings as a straight pay cut.

It is understood this view has gained ground in cabinet over the last few weeks as ministers have come in for some strong personal and political attacks at trade union conferences. New education minister and Tánaiste Mary Coughlan was on the sharp end of some heckling at the teachers conferences last month.

Also, justice minister Dermot Ahern was the subject of a barrage of personal and political abuse by the president of the Garda Representative Association, Michael O'Boyce, last week, so much so that the minister refused to address the conference on hearing of O'Boyce's comments.

The outcome of the vote on the Croke Park deal remains on a knife-edge, with the biggest public-service union, Impact, emerging as the union that will ultimately decide whether the deal gets over the line or not.

Based on the assumption that the union members vote in accordance with their executive's recommendation on the Croke Park deal, there are currently 990 Ictu delegate votes in favour of the deal and 910 against, with 690 as yet undecided.

Impact has 580 of the undecided votes at Ictu so its decision will now sway the vote one way or the other. Last month, the Impact executive caused a major shock when its executive decided that it could not recommend acceptance of the deal. This was despite the fact its general secretary, Peter McLoone, was one of the key architects of the Croke Park deal and had spoken about it as the best available in the current economic climate.

But McLoone has since called for "clarifications" which could allow the Impact executive to recommend acceptance of the deal. The executive meets on Thursday – the day after all public unions meet to consider Mulvey's proposals.

These two meetings will be critical to the fate of the Croke Park deal. But all members have yet to vote on the deal and as has happened before, they could vote against their executive's advice.

Either way, it appears the vote will be close. This raises the prospect of a large disgruntled minority. And nobody knows how they might act.