Payroll company Novopay may be hit in the pocket if teachers are successful with their legal action.

Teachers' unions PPTA and NZEI announced they're making the move after it emerged they won't get their pay rises until September.

Employment law specialist Catherine Stewart told Mike Hosking the court could impose penalties for a breach of employment agreement.

"There's a potential claims for interest, even possible claims for general damages, so there are other monetary values that can be looked at, as well as compliance."

She says it's a breach of contract issue.

"I think it's a fairly clear cut case of an employment agreement that's been entered into that doesn't appear to be being honoured."

Stewart says the teachers appear to have the support of the ministry, which also says the delays are unacceptable.

Auckland teacher Kahli Oliveira says teachers have been on the backfoot for a long time.

She says they've been looking forward to things like buying a new dishwasher or taking the kids on holiday.

Oliveira says Novopay was quick to take cash out when they took days off to strike, and she can't understand why it can't put money in as quick.