Bus drivers will be "working to rule" from 4am tomorrow and are warning commuters to expect delays and catch an earlier service than usual.

The strike will cause disruptions to Metrolink, North Star, Go West, Waka Pacific, City Link and Outer Link bus services.

The drivers claim their employer, NZ Bus, is increasing their working hours without providing toilet breaks.

President of the Tramways Union said from 4am tomorrow until an agreement has been reached, drivers will follow the rules of the company instead of taking shortcuts to make sure they kept to the timetable.

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This includes taking a 10-minute break at the end of each trip to conduct terminal duties, using a bathroom if needed and not waiting for their buses to be refuelled at the depots.

On the Link Buses, which are on a continuous loop, drivers will ask passengers to leave the bus while the driver uses a bathroom if needed, instead of waiting until the end of their five-hour shift.

School buses will not be affected.