Most Auckland bus drivers will begin strike action from September 17 after NZ Bus and two drivers' unions failed to reach agreement.

Mediation between First Union and the Tramways Union, who represent about 900 drivers, and NZ Bus, which runs the majority of Auckland's buses, finished without agreement on Tuesday, prompting the unions to announce the industrial action.

The drivers will now take strike action every Monday for nine weeks in an effort to get a claim for a $20 per hour pay rate to begin in July 2013 rather than April 2014, Tramways Union president Gary Froggatt says.

"Bus drivers are routinely away from home for 14-hour days to earn an eight-hour wage, due to their split shifts for peak services. It is not at all easy to support themselves and their families in Auckland on the wages that NZ Bus pay," he said.

"This is a very profitable company, who can comfortably afford a better deal for Auckland's bus drivers."

Pay rates covering shifts when drivers have to come in to work on their rostered day off are also at issue.

Mr Froggatt said NZ Bus' offer to pay them time and a quarter compared unfavourably to others in the company who get time and a half.

He said the impasse with NZ Bus was unfortunate given that First Union was able to settle with Auckland's other bus companies much more quickly.