The Association of Intermediate and Middle Schooling demanded a moratorium on changes to student-teacher ratios, after it initially feared that some intermediate and middle schools could lose up to seven teachers.
Association President Gary Sweeney said principals would withdraw their support from Ministry of Education initiatives and refuse to serve on a working party to implement the changes.
He said in his 20-year career as a principal, he had not seen such a response to change.
The Association of Intermediate and Middle Schooling, the School Trustees Association, the Principals' Federation, Secondary Principals' Association of New Zealand and the two teachers' unions will meet on Tuesday to decide on a course of action to oppose changes to student-teacher ratios.
Maori Party MP Te Ururoa Flavell said the party was disappointed the implications of the education policy were not identified in pre-budget briefings.
"We are concerned that sufficient details was not shared with us when we were briefed on the Budget and we will be advising the Prime Minister of our concern,'' he said.
He said the Maori Party were not convinced the debate was adequately informed by evidence about what the ideal ratio between teachers and students is, and how much it mattered to lifting achievement.
New Zealand First leader Winston Peters said the Government was creating a race-based education system which disadvantages the majority of New Zealand kids.
Mr Peters said there is a lack of transparency around the fact that class sizes will increase in mainstream schools but not in Maori Immersion schools.
"If smaller class sizes for Maori language immersion is intended to get better results then that should be the case for the remainder of the education system in which 80 per cent of Maori are enrolled,'' he said.
Labour leader David Shearer had ramped up his opposition.
"The Government's allies should use their combined political muscle to force National to ditch its plan to increase class size.''
Primary teachers around the country are mobilising this month to discuss options following the plans to increase class sizes.
Over 200 paid NZEI Te Riu Roa union meetings will be held around the country to discuss the teachers' collective agreements and topical issues.
Union spokeswoman Debra Harrington said following the Government's plans to increase class sizes in public schools, she expect the meetings to be well attended.
The issue of class sizes has been put on the table for discussion she said and could prove to be a "tipping point.''
Ms Harrington said teachers were "very, very angry,'' at the moment, "and that's why they're out on the streets.''
The meetings are to take place after school hours at 3.30pm so as not to disrupt student learning.
