The union representing bus drivers in the Hutt Valley says their industrial action could continue for weeks.
About 50 drivers employed by Tranzit, will be cutting their hours to a standard eight-hour day with breaks this morning, instead of the 14 hours that the union says they are rostered to do in some cases.
Today's action comes on the heels of drivers struggling to adjust to new timetables and bus routes last week, which caused delays and disruptions for commuters.
Tramways Union secretary Kevin O'Sullivan said the action would continue until they could negotiate a collective contract with Tranzit.
"We've been wanting to talk about a collective agreement. They signed an agreement, a formal settlement, to avoid appearing in the Employment Relations Authority that they would commence bargaining within seven days and that was six weeks ago, and we've heard nothing," Mr O'Sullivan said.
However, Tranzit managing director Paul Snelgrove said no driver working for Tranzit worked 14 hours shifts.
Tranzit said the industrial action taken by the bus drivers was punishing commuters and its own members.
Tranzit said today was always going to be a big day for drivers - with children returning to school from holiday - but the action would not have a significant impact.
The company said there were enough drivers and that they were committed to doing what was required to get everyone to where they needed to go.
On the other hand, Greater Wellington Regional Council councillor Daran Ponter said there might not be enough drivers to cover shifts if some drivers were to call in sick.
"We did have some difficulties with daily sickness last week, when that happens we then have to prioritise which services are cancelled on a strategic basis," Mr Ponter said.
He told Morning Report getting children to school on the first day of the new term was the main priority.
"It's a work-to-rule it's not a strike, so we're anticipating that if there are problems in the Hutt Valley those will materialise later in the day rather than the morning," Mr Ponter said.
"What we've done is prioritised the school bus services, remembering that for the first time in the network we're running a whole school bus network as well."
The real-time information boards have improved since technical difficulties last week plagued the network, and the apps tended to be more reliable for that information, he said.
"[Real-time information boards] have got better but there are services appearing on the board that then drop off two minutes beforehand," Mr Ponter said.
"The bus actually turns up but people sort of raise their hands in frustration as they should because they're immediate thought is the bus isn't going to be there."
The biggest issue faced by Tranzit and operators was the timing of buses on the new network, he said.
"If they don't do that you get a bunching of buses so you then get three buses at once and then you get nothing for 30 minutes and causes huge bottlenecks in the system."
He said that in time Tranzit could face penalties for those issues, along with NZ Bus, but they were operating in a grace period at the moment.