Secondary schoolteachers are to take industrial action over the revised public sector pay deal.
The Association of Secondary Teachers of Ireland (ASTI), which represents 17,000 teachers, has voted to reject the Haddington Road agreement and threatened a strike.
Teachers who cast ballots voted 63% against the pay deal.
ASTI general secretary Pat King said the message from teachers is that th ey have given enough.
"All second-level teachers are delivering more with far less resources at a time when their pay has been cut significantly and their working conditions have greatly disimproved," he said.
"The Haddington Road Agreement is a step too far. Second-level schools are at the tipping point, having been stripped of key supports and personnel.
"Young people's education has been diminished and their futures compromised. Haddington Road means taking more from education and from teachers."
The vote in favour of industrial action was 65% in favour of action up to and including a strike.
"Teachers are reluctant to take industrial action," Mr King said.
"However, the depth of feeling among ASTI members is evidenced in the ballot result on industrial action and this will be considered by ASTI standing committee at a meeting on Monday morning."
The Teachers' Union of Ireland (TUI) will announce the result of their ballot later tonight.
Gardai, nurses and civil servants have all previously accepted 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.
The Government had warned that it will impose unilateral pay cuts if unions do not support it.
The Unite trade union, which represents about 6,000 people in the public sector, was initially the only trade union to formally reject the deal but members later accepted the proposals in a re-ballot.
Members of Siptu, Impact, the Garda Representative Association (GRA), Association of Garda Sergeants and Inspectors (AGSI), Irish Nurses and Midwives Organisation (INMO), Psychiatric Nurses Association (PNA), and the Civil Public and Services Union were among those to accept the proposals over the summer months.
Elsewhere the Irish Fire and Emergency Services Association rejected it.
The TUI later accepted the Haddington Road Agreement by a majority of 54% to 46%, on a turnout of 65%.
General secretary John MacGabhann said his members voted with strong reluctance to accept "the lesser of two evils".
Gerard Craughwell, TUI president, added that the trust of teachers and lecturers in Government has been severely undermined.
"Notwithstanding the union's acceptance of the agreement there is a huge and growing sense of anger and frustration amongst teachers and lecturers at the fact that, as well as being targeted for successive pay cuts, they are being increasingly burdened with additional bureaucratic work that does nothing to enhance the quality of teaching and lecturing," he said.
"It should not be inferred that TUI's acceptance of Haddington Road represents an acceptance of the austerity agenda. It does not."