The ASTI has confirmed up to 17,500 of its members will withdraw from substitution and supervision duties in secondary schools from Monday.

Although teachers say they will show up for teaching duties as normal on Monday, it means 400 schools are now unlikely to open after the midterm break.

Boards of management had previously warned they could not open if all duties are not covered due to health and safety concerns, with the Department of Education issuing similar warnings.

The ASTI's announcement followed negotiations between the department and the teaching union in a long-running row over pay for recently qualified teachers.

The department and ASTI will meet again tomorrow.

A full strike day is scheduled for Tuesday, with five other strike days to follow over November and December.

ASTI President Ed Byrne said: “It was always inevitable that deducting pay from ASTI teachers for supervision and substitution work would lead to a withdrawal from this work. We made this clear to the Department as early as July of this year.

"Teachers received a commitment under the Haddington Road Agreement that this money would be paid. We delivered on all aspects of the Haddington Road Agreement. The Department’s decision to pursue this course of action is extremely problematic in terms of resolving this dispute.”

In a statement, the Department of Education said: "Department officials have remained in regular contact with the school management bodies on contingency arrangements ahead of the withdrawal of supervision and substitution from 7th November.

"However, at this stage it remains the case that widespread school closures are expected from the 7th November due to the ASTI’s industrial action and non-cooperation with contingency."