More than 2000 teachers could have debt collectors coming after them to reclaim the money they were overpaid when the payroll system switched to Novopay.
The Ministry of Education said staff have not paid a cent toward the $2.5 million they owe, and it was looking at ways of getting the money back. It would, however, consult with the sector before initiating debt collection.
Education Institute national secretary Paul Goulter said each case must be dealt with individually or there would be a rise in the number of personal grievances.
"Applying a one-size-fits-all and sending the debt collectors out after everyone is completely the wrong approach, it's wrong morally because Novopay was the ministry's cock-up in the first instance, and secondly it's an incorrect application of the law."
The Government was chasing teaching and support staff to try and reclaim the $45m cost of fixing Novopay, Mr Goulter said.