Nearly 60% of secondary schools will remain closed today as members of the Association of Secondary Teachers in Ireland withdraw from the supervision of students during breaktimes.
As a result of the action, ASTI members will not be available to carry out essential supervision duties before school starts in the morning, during break times, at lunch and at the end of the school day, the chairperson said.
The ASTI said it will continue to maintain contacts with the Department of Education and Skills tomorrow and in the coming days with a view to resolving the issues. "It is not acceptable", he said.
Noelle Moran from the ASTI says the government is trying to bully teachers into signing up to the Landsdowne Road agreement.
It's feared over 400 secondary schools - including some in Carlow and Kilkenny - will close indefinitely from Monday, if a row over pay isn't resolved this weekend.
Mr Bruton said he was bewildered by the teachers' approach.
If a school manages to stay open, ASTI members will be paid, even without doing supervision and substitution.
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He said if other public servants took the same stance as the Asti, it would cost the state 700 million euro (£623 million) or 14,000 jobs.
ASTI teachers voted earlier this year to stop working the hours 33 Croke Park hours.
School management bodies have urged both sides to come to a resolution for the sake of the thousands of students and families who will be affected. "We must get our schools open and our students back to their normal school routines as quickly as possible", he said.
Secondary school teachers are going on strike in a dispute over pay and conditions.
"Mine is the only school in Carrick in Suir that is closed as all the teachers in it are with the ASTI".
He said: "It is really about trying to bully us and our members into an agreement that they rejected".
Minister Richard Bruton says their refusal to join the Lansdowne Road pay deal is hurting newly qualified staff.