The Secondary Principals Association says it has had no notice of major bus strikes in Auckland that will affect thousands of the city's students.
More than 800 NZ Bus drivers are planning to strike every Monday for eight weeks, after rejecting a new pay deal from their employer.
NZ Bus operates services including Metrolink, Go West, Waka Pacific, Northstar and the inner-city Link routes.
A spokesperson for Auckland Transport, Wally Thomas, says about 9500 students rely on buses.
Mr Thomas told Radio New Zealand's Morning Report programme on Thursday that other operators are supplying extra vehicles and drivers when the strikes are on, but there is nothing it can do about school bus services.
"Their contract is directly with the Ministry of Education, so Auckland Transport can't impact that service, but certainly schools will be majorly affected."
But the principals' association says there has been absolutely no mention of the strikes.
Vice-president Paul Daley says he is surprised they have been planned without schools being notified.
"If this is a prolonged strike, then it's going to be very critical - particularly on senior students who are only with us for another four weeks in term four - and it's going to have a significant impact on their preparation for external examinations which will occur after that."
Auckland Transport says parents will need to make other arrangements to get their children to school and with so many more cars on the road, people should expect extra delays.
The Education Ministry says it is not yet able to comment on whether it will take any action to try to service school routes during the strike.