He achieved success as a singer, and his band Check 1-2 had a hit in Britain and Australia with the single "Mona" in 1990.
But she said that during Rocky Horror in 2014, McLachlan, who played transvestite Frank N Furter to her character Janet, he indecently assaulted her on stage during a sex scene.
Angela Scundi, who was an understudy to the role of Colombia in the production, told the ABC that GFO had been informed of the allegations.
Australian actor and musician Craig McLachlan has denied claims of indecent assault, sexual assault, exposing himself and bullying female colleagues.
"These allegations are ALL made up", McLachlan said in an email to Fairfax.
McLachlan has reportedly said he's never "done anything like this" adding he's in a relationship with a long-term partner.More news: New Kia Niro SUV revealed at CES
"He's a larrikin, up for a laugh and certainly, when we all first met him, that's indeed how he came across", she said. "We will be conducting a full internal investigation and will cooperate fully with authorities".
The fallout from the allegations also continued on Tuesday with the ABC withdrawing all episodes of The Doctor Blake Mysteries from its iView service and dumping a planned repeat screening of the Doctor Blake telemovie on January 25.
Now in Adelaide in support of the 2018 production of Rocky Horror Show, McLachlan slammed the allegations in an email statement as "baseless" and said "they seem to be simple inventions, perhaps made for financial reasons, perhaps to gain notoriety". An ABC spokesperson told Fairfax that "no complaints [were] made to the ABC involving any members of the Doctor Blake cast, who are employed by December Media".
The show's production company yesterday confirmed McLachlan would take no further part in the current production of the Rocky Horror Show after the accusations. A statement from Seven said they are now "seeking an urgent update from the producers". The women also said they feared for the current "Rock Horror" cast if they did not speak out.
Two of the women reportedly complained to senior production staff, but nothing was done.