The Public Service Association says workers deserve an apology from Education Minister Hekia Parata for what it describes as shocking and disrespectful comments about a pay glitch.
Ministry staff were not paid on their regular payday on Tuesday.
When Ms Parata was asked in Parliament about the error she joked it was 'karma' for the muck-ups with the Novopay system.
PSA national secretary Brenda Pilott says the comments, while off the cuff, are appalling and workers deserve an apology.
She says the Minister herself was ultimately responsible for the problems that have plagued the Novopay system.
The $30 million education sector pay system has been plagued with thousands of errors since it was introduced in August last year, with underpayments, overpayments or no payments at all to some teachers and school support staff.