She has claimed that while on stage with McLachlan and only visible to the audience from the waist up, he pulled up her underwear and kissed her buttocks.
Heynatz, who played Magenta and claims she was forcibly kissed by the actor, said: 'He's really calculated and very manipulative, a predator'.
Actress Angela Scundi, who has reported made a statement to police about an incident in which she says McLachlan had also made inappropriate comments about her breasts, played a Phantom in the musical and also an understudy for Colombia in Rocky Horror Show.
"I have NEVER done anything like this", he wrote.
It is not appropriate for December to respond to the allegations about Craig McLachlan's behaviour in relation to another production he has appeared in.
As well as starring in popular Australian shows like Home & Away and Packed To The Rafters, McLachlan released three studio albums between 1990-1996 and a number of hit songs such as Mona.
The "Rocky Horror" producers also said their records showed that none of the complainants had raised a complaint with the company in 2014.
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Craig has denied the accusations, saying in an email to Fairfax Media that the claims are "baseless" and "they seem to be simple inventions, perhaps made for financial reasons, perhaps to gain notoriety".
"He pushed his pelvis into me and moved around so I could feel his penis against my body", Scundi said. An ABC spokesman said they hadn't received complaints about Craig's behaviour while the show was being made.
According to The Sydney Morning Herald, Craig McLachlan has been accused of indecent assault, sexual harassment, indecent exposure, and bullying of female colleagues. I saw a different side come out in him which was terrifying'.
"We will be conducting a full internal investigation and will co-operate fully with authorities", GFO said.
The Victoria Police confirmed that detectives from Melbourne's Sexual Offences and Child Abuse Investigation Team are investigating the allegations.
"While we clearly can not comment on the details of this particular case, sexual assault in any form is unacceptable, and we will work diligently within this industry to support the right of all people to be protected in the workplace, and stand by those who are victims of inappropriate behaviour".
Production of The Doctor Blake Mysteries has also been put on hold "to allow due process", production company December Media announced Monday, and past episodes of the program have been removed from ABC's streaming platform iview.