A union whose members face pay cuts under the Croke Park II deal have rejected the proposed agreement.
The Association of Higher Civil and Public Servants has overwhelmingly voted against the deal by a majority of 85pc, with 15pc in favour.
The union, which has over 3,000 members, holds a 1pc share of the 20 public service unions’ votes.
Earlier, two unions representing construction workers and plasterers became the first to back the Croke Park deal.
The Building and Allied Trades Union, representing 125 construction staff, have voted in favour of the deal by 72pc to 28pc against.
It said a key factor was the fact that its members' basic pay would not be hit by the proposals.
OPATSI, which represents over 50 plasterers in local authorities, the HSE, OPW and Department of Defence, said 66pc voted in favour, with 34pc against.
"If this deal isn't accepted the first thing government will do is make staff compulsorily redundant, and I've no doubt they'll hit our members first," said General Secretary Billy Wall.
However, both unions are among the smallest of the public sector unions, and hold less than 1pc of the vote each.
The proposed deal, if ratified by all the public sector unions, will mean pay cuts for public servants earning more than €65,000-a-year.
It also means freezes and delays in the payment of increments, extra working hours, cuts in premium pay, and more flexible redeployment arrangements.
The Government has warned it will legislate for pay cuts, in the region of 7pc, for all 290,000 public servants if the agreement is not carried.
The final result of the unions’ ballots will be revealed this week, and the deal will be rolled out from July if ratified.
Three unions have already voted against the agreement, which aims to cut the state's payroll bill by €1bn over three years.
They are the Teachers' Union of Ireland, the Medical Laboratory Scientists Association and the Technical, Engineering and Electrical Union.
The Irish Federation of University Teachers and the Civil, Public and Services Union are due to issue their ballot results later today.
The two unions have recommended that their unions reject the proposals.
However, the results of the ballots of the unions with the greatest voting strength, IMPACT and SIPTU, will not be released until tomorrow at the earliest.
The final result will be revealed when the Public Services Committee of the Irish Congress of Trade Unions meets on Wednesday.