Primary school teachers and principals have voted for a full-day strike later this month.
NZEI Te Riu Roa principal and teacher members had already voted to strike for three hours on August 15, but yesterday decided to extend that to a full day.
NZEI lead principal negotiator Louise Green said extending the strike to a full day sent a strong message to the Government there needed to be better investment in education.
"Teachers and principals need to have time to teach, time to lead, and be valued for the professionals that we are. And all children need to get the support they need to thrive at school.
"We had a clear message from members at the paid union meetings and from feedback and surveys.
"It is 24 years since educators have gone on strike and this is not an action we are taking lightly."
Lead teacher negotiator Liam Rutherford said public opinion polling showed strong support for more taxpayer dollars being spent on education, including a significant pay increase for educators.
"The National Party's u-turn on teacher pay and new desire for smaller class sizes means there is now no political opposition to addressing the crisis in education."
The decision comes after NZEI and the Ministry of Education agreed yesterday to enter mediation over collective agreement negotiations.
The Ministry of Education had offered to increase pay, in the majority of cases, by between 2.2 and 2.6 per cent a year for three years.
The offer was a far cry from the 16 per cent increase teachers felt was needed to retain and recruit staff.
Ministry of Education Deputy Secretary of Early Learning and Student Achievement Ellen MacGregor-Reid said both parties wished to explore every possible avenue to reach an agreement.
"We value the work principals and teachers do and progressing these negotiations is a priority."
NZEI president Lynda Stuart said the union agreed to enter mediation "in an effort to explore all avenues".
"Negotiations are ongoing, and we are entering into the mediation in good faith," she said.
"Any outcome of the mediation will be taken back to NZEI members for their consideration."