Principals say cracks are starting to emerge in the new computer system designed to deliver the school payroll.
The Novopay system was introduced last week and principals fear there will be mistakes when it tries to pay about 90,000 people on Wednesday.
The switch to Novopay got off to good start when it spotted an error dating back 10 years that has cost the Government about $420 million in extra payments.
However principals complain they cannot get through to the Novopay helpdesk, payroll information is incorrect, and their staff have to spend a lot more time on the payroll.
Some fear Wednesday's payment of more than than $160 million salaries will be riddled with errors.
The Ministry of Education says all will be well. It has increased the help offered to schools and assured principals their staff will be paid on 5 September.