Te Riu Roa NZEI is looking at taking legal action following Novopay's announcement to teachers saying they would have to wait until September to see pay increases that they recently won when they settled their collective agreement.
Te Riu Roa says the lengthy delay from their settlement in June to September is "completely unacceptable".
NZEI Te Riu Roa National Secretary Paul Goulter says the union has instructed its lawyers to file action for compliance and penalties.
"We're taking every effort to try and force the Ministry to speed things up," he says.
In response to the delay, Education Minister Chris Hipkins called on education unions to work with the Ministry to simplify the system.
Goulter says the union is open to working with the Ministry to simplify the system, "on the strict basis that it won't erode any of the entitlements and conditions our members have fought hard for."
It comes after the mega-strike in May when around 50,000 school teachers took to the streets around Aotearoa, desperately calling for better working conditions and higher-paid salaries.
Primary school teachers accepted the $1.5bil offer in June.