The Education Minister Jan O'Sullivan says she will not have the money next year to try and tackle class sizes.
Pupil-teacher ratios had to increase in recent years, with an average class size of 24.4.
This is despite the government hiring some 2,300 extra teachers in 2013 and 2014.
Ms O'Sullivan has told the Dail any money she will have next year will be needed to hire even more teachers to deal with rising numbers of school children.
It comes as ASTI members have opted to extend the industrial action, sparked by plans to reform the Junior Certificate.
They are blaming a lack of training in advance of the changes, and they are also objecting to the idea of marking their own students' state exams.
Fintan O'Mahony is a teacher in Scoil Mhuire in Carrick-on-Suir, Co Tipperary. He says it is not fair.
