According to the email, Ritchies' management and the ORC, which is responsible for Dunedin public bus services, were undertaking a joint investigation into the driver.
"Ritchies management believe they have identified the driver concerned and he has been stood down from the service for the duration of the investigation," it said.
Ritchies Dunedin and Queenstown area manager Peter Varrie confirmed an investigation was under way, but referred all other questions to the council.
Multiple other complaints about inappropriate behaviour by the driver have also been posted on social media.
Asked if police had received any complaints about the driver on that route, a spokeswoman said they were "not able to respond to requests ... " without providing the date, time or name of alleged victim.