Teacher unions are holding 52 meetings nationwide over the next two weeks to discuss the Ministry of Education's proposal for a "global budget".

The New Zealand Educational Institute (NZEI) and the Post-Primary Teachers Association (PPTA) are concerned over the plan, which will abolish funding based on maximum classroom sizes in favour of flat funding per pupil.

But Prime Minister John Key and the Ministry of Education are emphasising the plan is nothing like bulk funding.

PPTA president Angela Roberts says the change could negatively affect the quality of teaching.

"It doesn't matter how good a teacher you are, you're an even better teacher when you don't have too many students in your class.

"It's critical to have good relationships, to be able to give really good feedback to students - you can do that much better with 25 students than with 35."

She says educators must understand the implications of getting rid of a strict teacher-pupil ratio.

But John Key says the funding model is not like bulk funding.

"This is crazy, isn't it? They're trying to rehash some sort of row," he told Paul Henry.

"Under bulk funding, you got the money whether you hired an expensive... or a less expensive teacher. That's not the case under this system.

"I think they just want to have a bit of a row with us."

New Zealand Educational Institute president Louise Green is concerned the changes will put teachers' salaries in competition with other costs.

"I'm saying that when push comes to shove, and boards of trustees and principals have to make tough decisions, they're going to have to manage their schools accordingly. We need guaranteed staffing."

Education Minister Hekia Parata says she's "somewhat surprised" the unions have come out in opposition to the system while discussions with their representatives are ongoing.

Both unions have members on a sector advisory board that's been discussing the proposals with the ministry since May.

Ms Roberts says the union meetings will be for teachers to learn about the proposed new funding model.

Union leaders will try to ensure disruption is minimal, Ms Roberts says, but the meetings are a priority.

"Schools will be able to have enough staff around to supervise, and make sure that kids can't be looked after elsewhere, that they'll be safe at school, but there certainly won't be as much teaching happening over the next couple of weeks."

About 60,000 teachers are expected to attend the meetings, the first kicking off at Auckland's Town Hall on Monday.

Newshub.