Education Minister Hekia Parata is "somewhat surprised" that teacher unions have come out in strong opposition to the Government's proposed new funding system for schools.
The PPTA and NZEI say their 60,000 members will hold paid union meetings next month to discuss a response to the "global budget" proposal.
They say it's a back door attempt to bring in bulk funding and larger class sizes, which has failed in the past.
Ms Parata says it isn't bulk funding and she's been discussing the proposal with the unions and other sector representatives since May.
"This is about flexible discretion for principals to decide what they need," she told reporters after the unions had held a press conference on Tuesday.
"The advisory group has been meeting in an open process since May and that is still in process, so I am somewhat surprised."
The unions say global funding means parents on school boards would have to make trade offs between the number of teachers they employ and other non-teaching costs of running a school.
That would encourage fewer teachers and larger class sizes, increased casualisation of jobs and further downward pressure on support staff hours and pay.
It would also remove the Government's responsibility for issues such as class size and curriculum breadth, they say.
Ms Parata says she'll continue talking to the advisory board of sector representatives.
Asked whether she would go ahead with global funding it in the face of union opposition, she replied: "We are the Government, we reserve the right to make decisions, but we're pretty keen to get informed feedback."
Labour and the Greens are backing the unions, and both parties refer to the proposed system as bulk funding.
"National should listen and back down immediately," said Labour's education spokesman Chris Hipkins.
"A return to bulk funding simply means larger class sizes."
The Greens' Catherine Delahunty says global funding would pose "impossibly tough choices" for schools.
"It will be very difficult for principals to make global funding work without cutting teachers, support staff, and administrative staff at a minimum," she said.