The Mana Party says the Government is pumping resources into private schools at the expense of state schools.
New teacher-student ratios in public schools announced by the Government in last month's Budget will result in increased class sizes and is aimed at saving $43 million a year.
Mana Party vice-president John Minto says the Government should be taking the money from increased subsidies it gives to private schools to give to state schools.
He says the extra $22 million Government funding to private schools this year allows them to keep class sizes to less than half that of public schools.
Mr Minto says educational achievement of Maori and Pasifika pupils, as well as those from poorer families, will be put at risk by larger class sizes.
He says it is very unusual for the education sector to be so unified in opposition to a policy and the level of dissent means the Government cannot ignore it.
"We've got a much more organised, coherent opposition to this policy and I think that will inevitably mean the Government has to back down all the way."