Education groups say they want more consultation about possible changes to the Education Act.
The Government is considering law changes that will make it easier for schools to vary their hours, and let a single principal run several schools.
The proposals are included in a discussion document presented to school leaders in May.
It says the Government wants to update the Education Act, following a taskforce that last year looked at the regulations affecting schools.
More on the proposals
The Secondary Principals Association said the changes would give schools more flexibility.
But the New Zealand Educational Institute (NZEI) and the Principals Federation said the Government needed to talk to sector groups before suggesting specific changes.
NZEI president Louise Green said the taskforce had recommended full consultation on the proposals, and that hasn't happened yet.
"We need to do that. And then once you've got that sorted, then you can talk about other issues and the details behind it," she said.
"But if you're talking about the details first, it is premature, and it's the wrong way to go about it."
Ms Green said the Government needed to first look at the purpose of the Education Act.
Education Minister Hekia Parata said the Government had discussed the proposals with the sector and there would be more consultation if it decided to go ahead.
She said the proposed changes to the Education Act were aimed at improving the standard of education.
Ms Parata said some schools struggled to attract and retain principals.
"Something like 40 percent of New Zealand schools have rolls of 100 or less, so we have small schools and generally they are in rural areas. So it's about how do we get the best resource to the kids who need it the most."
Ms Parata said the law already allowed schools to share a principal if they also shared a single board of trustees.