The Church of England has been urged to make an official stand against the "spiritual abuse" of conversion therapy for gay Christians.
The church's General Synod will on Saturday debate and vote on a private member's motion (PMM), urging it to oppose practices which claim to be able cure individuals of attraction to people of the same sex.
Christian gay rights campaigner Jayne Ozanne motion calls on the C of E to endorse a statement branding the therapy "unethical" with "no place in the modern world", signed by professional bodies including the Royal College of GPs and the UK Council for Psychotherapy in January.
The move is opposed by some conservative Christian groups, with one saying people seeking therapy want to "live full, Christian lives, within the natural order which God created".
Ms Ozanne, who herself underwent the therapy, told the Press Association it could ruin lives and in some cases drive people to suicide.
She said: "I call it abuse. I believe it is spiritual abuse.
"It (sexual orientation) is a very delicate area that only true professionals should be dealing with. And they won't try to change people's sexual orientation, they will help them try to deal with it.
"What people don't understand is that you can enter into this sort of practice willingly because you think it is the right thing to do because you have been told it is what God wants.
"It is only years later that the impact becomes apparent."
The Synod, currently meeting in York, has in recent years made headlines as the church tries to balance opposing views on homosexuality from its liberal and conservative wings.
The four-day assembly will also hear a motion urging churches to allow transgender Christians to renew their baptismal vows under their new name and identity.
The PMM says conversion therapy "is condemned by professionals as being harmful to LGBT people as it is based on a misguided belief that being lesbian, gay, bisexual or transgender is wrong".
It adds: "This leads to increased mental health problems for LGBT community due to stigmatisation.
"Given that many practitioners are non-medically trained religious leaders, it is imperative that the Church of England is unequivocal in its condemnation of such harmful practices."
In a briefing note on the motion, Synod secretary general William Nye wrote that there was no single definition of what practices constituted the therapy.
He added: "To the extent that individuals view themselves as offering therapy, whether or not they see themselves as 'practitioners', their practices ought to be held to the same standards as all health or well-being interventions.
"This means that they must meet rigorous criteria of safety, efficacy, ethics and prudence before being endorsed."
The motion was backed by Simon Sarmiento, chairman of LGBTI MISSION, which campaigns for gay rights within the church.
He said those who support the therapy were a small but vocal minority, adding: "They are against the whole concept of flexibility of sexuality or gender".
But Andrea Minichiello Williams, a lay member of General Synod and director of Christian Concern, criticised the motion, saying it had been "brought about on a purely emotional basis".
She said: "There are very many Christian counsellors and spiritual directors, as well as vicars and lay pastoral workers, who meet regularly with Christians with same-sex attraction.
"They do so because the person has come to them, and because they want to explore their sexual desires within the framework of the Bible and Christian discipleship.
"They are looking for pastoral and Godly help to enable them to live full, Christian lives, within the natural order which God created."