The Association of Secondary Teachers, Ireland (ASTI) is to ballot its members on industrial action, up to and including strike action.
The union is accusing the Government of failing to table a meaningful offer on public sector pay.
The previous public sector pay deal expired on 30 June, and formal talks have yet to begin on a successor agreement.
Similar ballots have been announced by other public sector unions.
Last week, Unite and the Prison Officers Association said their members in the public sector had voted overwhelmingly in favour of industrial action.
SIPTU will announce the results of its ballot later today, while Fórsa will outline its results tomorrow.
ASTI General Secretary Kieran Christie said public servants are working for less in 2026.
“The way to avoid industrial action is straightforward,” Mr Christie said.
“The Government must come to the table with a serious position on pay, honour existing commitments, and negotiate a fair settlement.”
“The ASTI stands ready to do that,” he added.
Minister for Public Expenditure Jack Chambers has said previously that the threat of industrial action is unnecessary and that the Government wants to reach an agreement on public sector pay.
A spokesperson for the Department of Public Expenditure said the Government remains available for engagement with unions on all matters.
“It is only through engagement that agreement can be reached,” the department said.
