Aucklanders wanting to catch a bus between 9am and 2:30pm today could face delays.
Drivers are taking industrial action, which will affect Metrolink, Go West, North Star, and Waka Pacific services.
Auckland Transport says there will be limited replacements on some routes while the strike takes place.
"We're working with other bus operators to provide a skeleton service on the routes that are affected and we've got them in place across most of the busier corridors across the city," says bus services manager Brendon Main.
The bus drivers are striking for toilet breaks on their shifts, and the New Zealand Tramways and Public Transport Union says drivers aren't receiving the treatment they deserve.
"We think that Infratil has been greedy with their tending, they've wanted to put more money in the shareholders' pockets and that's really not acceptable when it comes to jobs," says the union's Gary Froggatt.