The Irish Nurses and Midwives Organisation (INMO) is calling on their members to vote against the new Croke Park deal.
They are balloting their members on the agreement, despite walking out of the negotiations last Sunday.
The executive of the union say they believe the proposals are unfair and target those who cannot afford to pay.
Health Minister James Reilly urged them to stay in the process.
"I would say it is better to be inside the tent, negotiating a form to the agreement that is most beneficial to you - rather than to be outside and have others make those decisions for you" he said.
'Level of uncertainty remains'
The head of business group IBEC says public sector workers need to bear in mind the level of uncertainty that remains in the private sector when considering the extension deal.
A number of unions have already indicated their opposition to the deal.
Last night, the Teachers Union of Ireland (TUI) and the Irish Federation of University Teachers (IFUT) balloted their members on the new deal.
Their executive committees called on them to oppose the cuts to pay and pensions.
Speaking in Dublin today, Communications Minister Pat Rabbitte says speculation on the union process is not helpful.