But they say they are running the strike ballot to protect their members from potential disciplinary action, in case they are unable to reach agreement with the company on how many drivers should be rostered to stay at work to operate a "skeleton" bus service.
The ballot is due to run until Thursday, for votes to be counted by the weekend.
One company employee claimed drivers were voting "in favour of direct action" in the ballot.
But First Union organiser Rudd Hughes said tonight that efforts would continue to run a stopwork meeting without having to declare it as a strike.
He said the meeting would be timed for when many drivers were "booked off" duty in any case, under split shifts, so he could not understand the company's concern.
"We are struggling to see what the problem is," he said.
The company could not be reached for comment.
As well as being apart on wages, with the unions seeking a 2.95 per cent rise against a company offer of 0.75 per cent, the parties are at odds over major roster changes made in July requiring most drivers to work rotating shifts.