The country's lowest-paid public servants will take industrial action if the Government enforces pay cuts, their union has warned.
Civil Public and Services Union (CPSU) president Joan Byrne said workers would fight if Public Expenditure Minister Brendan Howlin refuses to bin the cuts.
"We have had enough, we are prepared to fight," Ms Byrne said.
"We have shown before that we can and will take action, we won't lie down quietly while they walk all over us. We have the strength, the mettle and the means to fight. We do not want to have to take industrial action, but be under no illusion minister Howlin, we will fight if you don't bin these unfair cuts."
Several unions overwhelmingly rejected pay cuts and reforms under Croke Park II, prompting Mr Howlin to ask one of the country's top industrial relations mediators to see if there are grounds for a re-run of negotiations.
Ms Byrne applauded CPSU representatives for walking out of pay talks with the Government when it became clear that no real changes to the deal were possible. "The huge response by our membership in our recent ballot verifies the membership's support for their decision," she told delegates at the union's annual conference in Galway.
"Our overwhelming 'No' to Croke Park II supports their efforts on all our behalf. By our actions, we have set down our marker loud and clear, we have endured enough, we are strong and we are united along with other unions who have the same message for the Government."
Despite the complete collapse of the first deal, the Government has said it is committed to taking 300 million euro off the public sector pay and pensions bill this year, and one billion euro by 2015.
Earlier this week, Mr Howlin revealed plans to ask Labour Relations Commission chief executive Kieran Mulvey to contact union leaders to see if they are willing to reopen negotiations on cost-cutting.
The Teachers' Union of Ireland (TUI) has already insisted it will not re-enter talks. Among the unions to vote against the first deal - despite Mr Howlin's threat of unilateral pay cuts and reforms - were the TUI, the Irish National Teachers' Organisation (INTO), the Association of Secondary Teachers' of Ireland (Asti), Siptu, the Irish Nurses' and Midwives' Organisation (INMO) and the CPSU.