Hundreds of secondary schools across the country are to remain shut indefinitely after crunch talks over a pay row collapsed without a deal.
Education Minister Richard Bruton said he is very disappointed last gasp negotiations with the Association of Secondary School Teachers' of Ireland (Asti) over the weekend failed.
"This will cause huge disruption for 200,000 students, and their parents, with particular stress caused for those in exam years," he said.
"Asti have effectively decided to close hundreds of schools indefinitely, as a result of a dispute which essentially relates to one hour a week of additional duties.
"Monday's withdrawal from supervision and substitution duties, and consequent closure by Asti of hundreds of schools, is explicitly not about new entrants pay, but about the Croke Park Hours - one extra hour each week for the 33 weeks of the school year."
Asti has said its 17,500 members will refuse to carry out supervision and substitution duties as part of the industrial action over pay for supervision as well as equal wages for recently qualified teachers.
More than half of the country's 735 schools face closure as a result.
In a statement, the union said it is "regrettable" that the planned withdrawal from supervision and substitution will go ahead, citing "no progress" on key issues.
"Teachers who are members of the Asti will turn up for work as normal tomorrow but will not engage in supervision and substitution duties," the statement said.
The union said it will continue contacts with the Department of Education and Skills in the coming days.
Mr Bruton insisted a "good deal" is already on the table.
"I would again urge Asti to consider it seriously, so that we can end this dispute and limit the disruption to parents and students," he added.
"I am also disappointed that the Asti refused to cooperate with any contingency plans, both not allowing their principals to co-operate, and by not giving schools enough time to advertise, recruit and have external supervisors Garda vetted.
"As a result, hundreds of schools will be forced to close tomorrow to protect the health and safety of students and staff".