The Government's one billion euro public-sector pay-cut plan has further support after another important union gave its backing.
Three-quarters of Siptu members working for the State voted in favour of supporting the Haddington Road agreement.
The deal, the successor to Croke Park, will see public sector pay cuts of 300 million euro this year and one billion euro over three years.
Siptu vice-president Patricia King said the next step was about implementing reforms.
He added: "We welcome the result of this ballot which followed a period of consultation and discussions among our members in the public service.
"We now hope that we can move on to implementing the reform process in order to improve the services for those who depend on them while protecting the jobs, terms and conditions of those who provide them."
Siptu workers join the Irish National Teachers' Organisation, the largest teaching union, in supporting the proposals.
The executives of the Association of Secondary Teachers' of Ireland and the Teachers' Union of Ireland have rejected the Haddington deal and not put it to a ballot. The Unite trade union, which represents about 6,000 people in the public sector, put it to a vote and members refused to support it.
The Government has warned that it will impose unilateral pay cuts if unions do not support the Haddington Road Agreement.
The Irish Nurses' and Midwives' Organisation is expected to announce its ballot on Friday.