Schools are worried a court ruling could unexpectedly leave them facing higher costs for teachers to attend events such as camps and overseas trips.
The Employment Court ruled in favour last month of 11 current and former staff of Iona College and Woodford House, who worked as boarding supervisors.
Often sleeping over at the premises, they claimed to have worked up to 140 hours a fortnight, including 40 to 60 hours during sleepovers.
They were paid $25 a night for a non-rostered sleepover, but it was argued they should have received the minimum wage.
The court agreed, and ruled the staff were able to claim backpay, which is likely to be in the hundreds of thousands of dollars.
Other boarding schools could also be affected, with some also concerned the ruling could be interpreted more broadly than intended.
Scots College principal Graeme Yule said the decision would not affect its boarders as it employed a matron who lived in her own house.
But the ruling could have a wider impact, as it was unclear if schools would have to pay the minimum wage for overnight stays on camps or trips overseas.
Staff were paid an overnight allowance at present, but extra costs would put a strain on schools. "It opens up a whole raft of potential issues, so we're standing by, and I hope common sense prevails."
Woodford House board of proprietors chairman Phil Williams said the schools had filed for leave to appeal. He agreed it was unclear what impact the ruling could have, and both schools were working through the court's decision.
It had the potential to cost a significant amount of money, so it was important the law was interpreted correctly.
In a written statement, Iona College acting principal Julie Shears said the financial impact on boarding schools would vary depending on their situation, but could be significant. If the leave to appeal was granted, she would encourage other schools to support them.
The Service and Food Workers Union, which took the case on behalf of the staff, said it would fight the appeal application.
National secretary John Ryall was dubious the case could lead to unforeseen problems.
"When we were dealing with the [rest home sleepover] case, the argument from the Crown and the employers was that the whole sky will fall in, it will have major ramifications for the whole economy - but that turned out to be untrue."
- The Dominion Post