Secondary schools may close for a day after teachers voted to extend industrial action over plans to reform Junior Cycle education.
Members of the Association of Secondary Teachers Ireland voted overwhelmingly in favour of strike action, including a one-day strike.
The vote was 84% in favour of action.
ASTI General Secretary Pat King said the results showed the depth of feeling among the union's members.
He said Minister for Education Jan O'Sullivan now had a clear message that teachers were not prepared to implement proposals which they believed were educationally unsound.
The new Framework for Junior Cycle is being implemented in schools on a phased basis from this school year.
ASTI members have already agreed to not cooperate with the implementation of the new framework.
The new proposals include the abolition of the Junior Cert exam and its replacement with school based certification.
Teachers are unhappy with the fact that the new system will be based on exams set and marked by students' own teachers.
The ASTI is the largest union representing post primary teachers.
Its sister union, the TUI, has already voted for industrial action up to and including strike action.
In a statement the Department of Education has said the minister is considering the concerns of teachers which have been raised with her at meetings with their representatives.
The Department says Jan O'Sullivan is looking forward to a follow-up meeting with the teaching unions later this month, to further progress discussions.
The statement went on to say that the unions had underlined to the minister teacher support for reforms that will lead to better quality teaching and learning experiences for students.
