Times are tough for principals, struggling to up the wages of underpaid support staff.

Schools' operational grants got a 1.3 per increase in last week's budget, but principals say that's not enough.

500 principals have signed an open letter to the Government asking for the change - as negotiations get underway.

NZEI president Lynda Stuart told Mike Hosking more than 20,000 support staff could have their hours cut if grants don't get a boost.

"We need to see that any pay increase for their support staff is actually funded through into the operations grant directly," she said. 

The cut back would impact staff in schools throughout the country.

Stuart said principals are speaking out on behalf of underpaid staff.

"These people are among our lowest paid people within the education sector, it's really timely that our principals say well this is the reality for us," she said.

LISTEN ABOVE: Lynda Stuart talks to Mike Hosking