Andy Meddick from the Animal Justice Party, Reason Party MP Fiona Patten and Samantha Ratnam of the Greens confirmed on Tuesday they will back the Change or Suppression (Conversion) Practices Prohibition Bill in the Legislative Council.

The bill outlaws any therapy that attempts to change or suppress a person's sexual orientation or gender identity and empowers the Victorian Equal Opportunity and Human Rights Commission to investigate reports of conversion practices.

It also puts in place strong criminal sanctions for people who subject others to conversion practices that cause injury or serious injury, with up to 10 years' jail for the latter.

Those who try to get around the laws by sending people to conversion practices out of the state would also face criminal sanctions and fines to a maximum of almost $10,000.

Mr Meddick, in supporting the bill, described himself as the proud father of two transgender children.

"I love them and I support them. And to all those who are detractors to this bill, I have a message: This bill will pass," he said.

"For all of the community out there ... I have another message for you: I see you, I love you and I support you."

The bill goes further than a similar law passed in Queensland last year, by prohibiting harmful practices not only in healthcare settings but also in religious settings.

It bans "carrying out a religious practice including but not limited to, a prayer based practice, a deliverance practice or an exorcism".

A number of religious leaders have raised issue with the bill, including Melbourne's Catholic Archbishop Peter Comensoli and Bishop Brad Billings of the Anglican Diocese of Melbourne.

"(The bill) has some potentially serious unintended consequences in respect to fundamental human rights such as the freedom of speech, the protection of religious belief and freedom of conscience," Bishop Billings said in a statement to AAP.

"It potentially criminalises the provision of pastoral care and may limit the ability of parents to guide their children."

Islamic Council of Victoria vice president Adel Salman said a number of faith groups had not been consulted in the drafting of the bill.

"There's overreach there that impinges on the rights of individuals to practice their faith freely, for people to seek guidance, for parents to parent," he told AAP.

"Some of these things potentially could have been avoided if we had been part of genuine consultation."

The opposition said there were also concerns within the medical community that the bill could compromise the practice of psychiatry and psychotherapy.

"As it currently stands, the bill would mean medical professionals would be unable to provide full and frank professional opinions to their patients and could risk up to 10 years' imprisonment for doing so," Shadow Attorney-General Edward O'Donohue said.

While Mr O'Donohue said the coalition supported the banning of "barbaric" conversion practices, they wanted the government to pause progress on the bill to further consult with stakeholders.

The opposition will also seek to amend the bill to rein in powers proposed for the Victorian Human Rights and Equal Opportunity Commission.

Ms Patten, however, said she was comfortable with the legislation as it stands.

"This bill is about freedom for all, not just a selected few who feel that their religion trumps other people's lives," she said.

Ms Ratnam said a lot of the arguments against the bill were "inherently homophobic and wrong".

"It's hard to fathom that we're even debating this matter in this parliament because it implies that there are valid arguments on either side of this debate when clearly there aren't," the Victorian Greens leader said.

The bill will be debated in the Legislative Council on Thursday.

Australian Associated Press