A Wellington bus union says Tranzit is restricting access to its members but the company's managing director says the allegation is "ridiculous".
Police were called about two men trespassing at two Tranzit bus depots yesterday after union representatives arrived outside the depots to meet members.
Tramways Union advocate Graeme Clarke said they were conducting a ballot with members outside the property.
The issue had already been resolved once police arrived.
Mr Clarke said they were forced to meet members at depots because they could not get access any other way.
"This company won't allow normal right of entry procedures to apply and they certainly wouldn't cooperate with the stop work meeting," he said.
"We don't even bother to ask them because they will not allow people to meet and exercise union rights. They're anti union."
Tranzit were trying to limit discussions by requiring someone from management to accompany union officials at all times, Mr Clarke said.
Tranzit's managing director Paul Snelgrove said this was not true.
"That would be absolutely dead against our company policy," he said.
"If anyone wants to talk to a union they can, they certainly wouldn't have any management or a director standing there while they spoke to the union. That is just a straight out allegation, that's ridiculous.
Tranzit is open to a collective agreement but would not tolerate harassment of staff, Mr Snelgrove said.