Meanwhile, after two hours of delays the service was restarted but not without incident, according to First Union, which represents some bus drivers.
It is alleged two senior Go Bus managers got into buses and attempted to drive through the blockade of striking employees.
However, in a statement, the bus company sternly denied accusations it put the picket line at risk of injury and said it was those on strike who had been out of control.
It also asked for First Union and its members to dial down the hyperbole and aggression.
"The union's decision to attempt to disrupt bus services on the first day of NCEA examinations shows just how out of touch they are with real people," said Kura Poulava, HR director of Go Bus Transport.
"Right now is a particularly stressful time for students and their parents, and the action of First Union is exacerbating this stress.
"We respect the right of the members of this union to strike and picket but implore them not to interfere with our lawful efforts to provide a reliable and safe bus service and ask them to think about our student passengers at this time."
The strike took place amid talks between the union and Go Bus over fair wage bargaining, a dispute which first started in May, 2019.
Bargaining is set to begin on Friday, around a fortnight after the bus company agreed to enter negotiations with drivers and the union.
The blockades kicked off around 7am, Auckland Transport told the Herald, with services first getting started again around two hours later.
"AT and Go Bus's priority was the school bus routes, making sure that any student who was able to catch the service to school [was catered to]," AT said in a statement.
"The union was blocking the road, not allowing any buses to leave, which included non-union drivers and several other transportation companies that used the road.
"We find this very disappointing, because this was timed to interrupt the school bus routes."
Drivers also alleged they had faced hostility from managers before, First Union spokesman Jared Abbott said.
"This morning's dangerous bullying behaviour from senior Go Bus managers shows that all they care about is their bottom line," he said.
"Not the people driving their buses for years, not the public, just their company's profit."