The union representing secondary teachers says schools should ignore advice from the Ministry of Education about how to implement the new legal entitlement to rest breaks.
The PPTA is at odds with the ministry over guidelines on how to implement the new legislation which were sent to schools on Wednesday.
The union says the guidelines are unclear and do not protect teachers' working conditions.
The PPTA says the main stumbling block is whether non-teaching time can be used for breaks.
Union president Kate Gainsford says the two must be regarded as separate entitlements and one cannot be used to prop up the other.
She says the non-contact time was an attempt to address teachers' workload and was very hard fought for.
The Secondary Principals Association believes the guidelines allow for non-teaching time to be used for breaks and this is the right course of action.
In a statement, the Ministry of Education said it is disappointed it has been unable to reach an agreement with the PPTA and will continue to work on the issue.