"Either we're in a social partnership or we're not," the SIPTU president, Mr Des Geraghty, said yesterday, after confirming that his union was withdrawing from talks on a successor to Partnership 2000 to review its position in the light of the Budget.
"When we signed up to the NESC (National Economic and Social Council) report it was on two bases - that the social partners would work together to maintain economic advances and that there would be a significant redistribution of rewards."
He said the question of what the union's bottom line would be was a matter for the executive when it met during the next two days.
It is no secret that one of SIPTU's main objectives is to secure large increases in the £1,000-a-year PAYE allowance. That would have benefited all workers, but particularly low and middle-income groups, including women returning to the workforce.
Mr McCreevy did meet one of the main demands of the trade union movement in removing people on the average industrial wage from the top tax bracket. On that basis the ICTU gave a qualified welcome to the Budget.
It was a response that several senior trade union leaders have been saying privately was the wrong one. Now SIPTU is saying it loud and clear and, because it represents 200,000 of ICTU's 500,000 members in the Republic, it is a voice that will have to be listened to.
Earlier, the SIPTU regional secretary for the midlands and south-east had already raised the spectre of withdrawal from the talks. "I cannot see how an agreement can be brokered now, in the light of this Budget, which is clearly biased in favour of the better off," Mr Jack O'Connor said. "Thousands of workers on less than £280 a week hardly benefited at all, while those on £50,000 plus benefited most."
Nor is SIPTU alone. Impact's general secretary, Mr Peter McLoone said last night he believed an urgent meeting of ICTU was needed. "The Budget presents huge problems. As far back as 1997, we made it clear the main beneficiaries of economic growth had to include the low-paid. This budget has thrown everything we have been doing for the past couple of years out of sync."
Unions such as Mandate, which has thousands of shop workers in the retail trade, and the ATGWU, which represents large numbers of blue collar workers in the private sector, make no secret of their frustration at the way low-paid groups have been left.
At the union's biennial conference in October, Mr Geraghty won support for entering the talks on the basis that the low-paid would be looked after. The NESC report, which was almost completed at that stage in joint discussions with the Government and employers, was a central component of the approach adopted by all the social partners, he said.
On Wednesday, Mr McCreevy kicked one of the main props away, nor has the concentration of the debate on the double-versus-single-income earning households helped. SIPTU's latest move is clearly aimed at concentrating minds on the wider agenda and is likely to succeed.