The Labour Party says the decision to roll out Novopay has cost taxpayers as much in six months as it would have cost to keep the previous teachers' pay system running for six years.
The system has made thousands of mistakes in teachers' pay since it was introduced in August last year and the Government is spending millions on fixing problems and recompensing schools.
Labour's education spokesperson Chris Hipkins says a Ministry of Education memo shows the minister calculated in May last year that it would cost an extra $12 million to keep using the system developed by Datacom.
Mr Hipkins says in the last two weeks alone the Minister Responsible for Novopay, Steven Joyce, has thrown $11 million at fixing problems within the system and compensating schools for the extra work they've had to do.
He said spending on the ministerial review of Novopay and on the technical review bring the total to nearly 12 million dollars.