The primary teachers' union says the government needs to be fair when collecting money owed by school staff.
The Novopay Minister Steven Joyce has called in debt collectors to recover $1.8 million from almost 2000 teachers and other school staff overpaid during the Novopay school payroll debacle.
After the system was introduced in 2012, many teachers and other staff were under-paid or over-paid.
The Educational Institute's president Louise Green told Morning Report it was understandable to expect the money back, but the government needed to be reasonable.
"What's important is that people actually have an opportunity to see what the debt is, and to correct if it's wrong and accept it and then have some reasonable payment rates.
Ms Green said staff who were still employed should be dealt with face-to-face.