NZ Bus says it has twice agreed with unions on a new pay offer, only to have the deals voted down by members.
The company's Auckland drivers have rejected the latest pay deal in an ongoing dispute and will work to rule from Friday.
Their unions say more than 60% of drivers must accept the deal for it to be ratified.
NZ Bus says it has agreed with the unions on a fair deal, and at some point it needs to move forward as a business.
The company says it intends to continue trying to conclude the bargaining.