Teachers in Tyrone and Mid Ulster are set to go on strike over a pay dispute on 31 January, forcing the closure of local schools, it is expected.
The rolling day of action is being held by the National Association of Schoolmasters/Union of Women Teachers (NASUWT) members.
It follows a walk out in Belfast and Newtownabbey on 30 November.
The row is centred on the rejection of a 1% pay raise for this year being rejected by teachers, with no rise being offered for 2015/16.
The Education Minister Peter Weir has said that the only way to achieve a raise for the previous year is through redundancies.
NASUWT general secretary Chris Keates said: “It is with deep regret that we remain in this position, but we have been left with no choice by the blatant disregard of the minister for education and the employers for the pay and conditions of service of teachers who provide such a vital public service.
“We have continued to make clear to the minister that strike action can be avoided if there is an improvement on the 0% pay award for 2015/16 and a genuine commitment to meet with the NASUWT to seek to resolve our trade dispute.
“If the next phase of strike action goes ahead, it will be the responsibility of the ministers and the employers.”
The strike is likely to force the closure of the majority of Council for Catholic Maintained Schools in the area and some primary schools.