Conservative American commentator and author Eric Metaxas, a keynote speaker at Saturday's event in Sydney, is also a supporter of gay conversion therapy and claims "normalising" homosexuality is an attempt to break down all sexual boundaries.

In a 2011 interview he drew parallels between the current push for equality and the Church failing to stand up to the Nazi party.

Another star attraction, Jeffery Ventrella, is a leading attorney with the US Alliance Defending Freedom – a Christian legal juggernaut bankrolling an international push to restrict LGBTI rights – who believes homosexuality is a "profound risk" to physical and mental health.

Earlier this year former prime minister Tony Abbott came under fire for appearing at an Alliance event in the United States to give a speech on family values.

Gay rights leaders have called for the Treasurer to pull out of the event and have warned that the Australian Christian Lobby's alignment with the US group is a sign it plans to step up its campaign against the LGBTI community.

"This is a group that is leading the legal fight to deny the human rights of LGBTI people around the world and we should all be deeply concerned that they are being paid by the Australian Christian Lobby to appear here, particularly as we prepare for what could be a very damaging plebiscite on marriage equality," said Victoria's Gender and Sexuality Commissioner, Rowena Allen.

Ventrella has stated that "homosexual behaviour carries with it profound risks not only to one's body, but also to one's mind and emotions".

Australian Christian Lobby managing director Lyle Shelton defended paying for Mr Ventrella's appearance at the "Cultivating Courage" conference, saying it was becoming harder to be a Christian in Australia.

"If this is where it's going that it's no longer tolerated that you can hold the view that marriage is between a man and a woman then obviously we're going to need legal representation to protect those freedoms and that's why we've invited ADF to our conference."

The Alliance Defending Freedom has assisted on cases that affirmed the right of St Patrick's Day Parade organisers to exclude LGBTI groups and to allow the Scouts to discriminate against gay members.

Greens spokesman for LGBTI issues Senator Robert Simms said the views of the speakers were "reprehensible" and he was disturbed that the Treasurer, an evangelical Christian, would share the rostrum with them.

"Politicians need to no longer legitimise hate campaigns of these kinds of organisations. The Australian Christian Lobby have been leading Liberal Party policies for years and it's quite clear that Malcolm Turnbull is equally as captive to them as his predecessor," he said.

Religious groups are pushing back against equal rights, with the Catholic Church last week pressuring Telstra into backing away from its public support for marriage equality.

In March, the ACL successfully led a push for the Turnbull government to gut Safe Schools – a program to make classrooms safer for same-sex attracted and gender diverse students.

Sean Mulcahy, co-convenor of the Victorian Gay and Lesbian Rights Lobby, said the Alliance Defending Freedom did not represent the majority of Christians and their public statements were "incredibly damaging" and had no basis in fact.

Ali Hogg, convener of marriage equality group Equal Love, said the group was planning protests at the "Cultivating Courage" conference and have called on Mr Morrison to pull out.

Other conference speakers include News Ltd columnist Miranda Devine and Aboriginal leader Noel Pearson.

In 2014, Opposition Leader Bill Shorten used his appearance at the ACL conference to make a case for marriage equality and argued that freedom of worship did not mean freedom to vilify.

Mr Morrison declined to respond to questions about the views of Mr Metaxas and Mr Ventrella. "There is a long tradition of political leaders of both sides of politics attending and speaking at ACL events," a spokesperson said.

With Adam Gartrell

jstark@fairfaxmedia.com..au

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