More than 700 Board of Trustees chairs have signed an open letter to the Government calling for a better pay deal for school leaders.
The letter, published by 762 people in total, was published in 11 newspapers on Thursday morning.
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It called for a new deal for principals that includes pay parity between primary and secondary, which teachers were granted in June.
New Zealand Educational Institute president Lynda Stuart told Newshub the response has been huge.
"As I was leaving the office there were more signatures coming through they just didn't meet the deadline to get in the newspaper.
"So what we're seeing is that groundswell of support for our school leaders."
Stuart says rural schools are especially concerned about losing their principals, fearing they may go to better-paid roles.
"If those people decide that they're going to move into a larger school in a senior leaders role and actually potentially earn more money, then who's going to go and lead those small schools?"
She's glad so many people signed the letter, saying it should send a clear message to the principals.
"It has given our boards of trustees the opportunity to show really how valued their principals are to them."
Principals are taking partial strike action by ceasing Ministry related work. They rejected the last pay offer in June, at the same time primary teachers accepted their offer.
Chris Hipkins said at the time he was disappointed in the result.
"We were very, very clear with both unions…that this was a final offer,” Hipkins told Newsroom.
"If they want us to reconfigure the offer within the amount of money that's available...we are always open to talking about that. Always have been. But there will not be any more money for principals in this round."
The offer would have given principals a lump sum payment $1500 and a 3 percent pay rise on July 1, followed by subsequence increases of at least 3 percent after 12 months and 24 months.
It also had specific support for principals in schools with less than 100 students and would have allowed them for 10 hours per term of classroom release time from 2020m and increased operational funding to allow for two fulltime equivalent staff for schools who currently have an entitlement to fewer than two fulltime equivalent teachers.