Yesterday the NZEI announced it would not engage in collective negotiations, in an attempt to shape how the reform will take shape.
Ninety-three per cent of its members who voted said they had "no confidence" in the Government's plan.
Mr Key kicked-off National's election year in January by announcing the IES policy, which will cost an extra $360 million over four years.
The scheme aims to identify the best principals and teachers and pay them more to spend time in other local schools or provide an example within their own.
Schools that are struggling can also ask for an allowance of $50,000 to top-up the salary they can use to attract a principal.
The four new roles would work across a cluster of 10-12 schools. Schools that do not want to be involved can opt-out.
The leadership of NZEI has been a vocal critic of the policy, arguing the money would be better spent on helping lower decile schools cope with children damaged by poverty and neglect.
Union president Judith Nowotarski said the policy had been proposed without the involvement of schools or parents, and with no evidence that the new model would help student learning.
Yesterday's rejection of IES is less likely to be repeated at the secondary school level.
The Post Primary Teachers Association and the Government have been working through detail of how the new roles would work, and pushing for some changes.
Its executive has been supportive of IES, and negotiations are ongoing on the teaching roles associated with secondary schools. Agreements had been reached with organisations that represent the principals of New Zealand's 339 secondary schools, as well as the NZ School Trustees Association.