Two major teachers' unions are joining forces to fight the government's planned overhaul of the school and early childhood funding systems.
The Educational Institute and the Post Primary Teachers Association (PPTA) have announced they will hold joint meetings for their 60,000 members to discuss the government's plans.
The unions said they had never held joint meetings on this scale before.
Their leaders said they wanted a mandate to oppose a government proposal that would let schools sack teachers and use the savings to buy computers or hire teacher aides.
The proposal - called global funding - was at the heart of the government's plan for overhauling the school and early childhood funding system.
It would let schools exchange teacher positions for money they could spend on other things.
Educational Institute president Louise Green said schools did not have enough funding and the proposed system would lead to choices that would hurt the quality of education.
"There's a good chance that teacher salaries would be traded off so that other costs can be met. And when teachers are traded off then class sizes will go up, curriculum choices can be restricted, unqualified teachers could be employed because they're cheaper, those kinds of things."
PPTA junior vice-president Jack Boyle, a Hutt Valley teacher, said teachers of subjects that provided breadth in the curriculum, but attracted relatively few students, would be at risk.
"Amongst teachers there is a very real concern that those teachers in smaller subjects will suddenly be on pretty shaky ground," he said.
"So, for instance, you tend to get lower levels of student participation in subjects like music, like ICT, like the performing arts subjects, and languages. Those subjects potentially are at risk."
PPTA president Angela Roberts hoped the unions were not on a collision course with the government.
But she said it needed to know that its plans for the funding system were a bad idea.
"The opportunity for the government to make one massive mistake that is going to have repercussions right across the sector is significant and somebody needs to stand up and tell Cabinet they are heading off in the wrong direction."
Ms Roberts said the government had indicated it would not push ahead with plans if the education sector opposes them and she hoped it would stick to its word.
Education Minister Hekia Parata said the government was still in a process with education sector groups and she was disappointed and surprised by the unions' actions because the proposals were still under consultation.
She said the global budget scheme based funding for teachers on a notional average, so that schools would not be financially better off if they replaced older, more experienced teachers with new, cheaper teachers.
The Secretary for Education, Katrina Casey, said the global budget was a way of giving schools more flexibility with their resources.
She said no decisions on the funding review had been made.
"The discussions about these funding review proposals haven't even finished yet. Once they do, we will take into account all the views expressed before providing advice to the Minister."
The unions said their meetings would be held during a two-week period, starting on 5 September, and were likely to result in some disruption to school opening hours.