Over 500 church leaders from across the UK have written to the government to say they are prepared to face criminal charges if a conversion therapy ban is introduced.
In the letter, they say that they will "continue to do our duty to God" even if the proposed ban comes into force.
"It should not be a criminal offence for us to instruct our children that God made them male and female, in his image, and has reserved sex for the marriage of one man and one woman. Yet this seems to be the likely outcome of the proposed legislation," they write.
"We therefore very much hope (and pray) that these proposals will be dropped in their current form. We have no desire to become criminals, and place a high value on submitting to and supporting our government.
"Yet we think it important you are aware that if it were to come about that the loving, compassionate exercise of orthodox Christian ministry, including the teaching of the Christian understanding of sex and marriage, is effectively made a criminal offence, we would with deep sadness continue to do our duty to God in this matter."
The open letter, which is still collecting signatures online, has been sent days before a government consultation on the proposed ban ends on Friday. Christians are being urged to participate in the consultation to make their concerns known.
Dr Ian Paul, a theologian and member of the Church of England's General Synod, said the current proposals were "ill considered and ill conceived".
"As the consultation document itself states, many of the issues highlighted are already illegal," he said.
"The term 'conversion therapy' is ill defined, and the proposals appear to be driven by an ideological agenda rather than real concern and clear thinking.
"There is a real risk that pastoral ministry will be criminalised, and that human rights, including the right to religious belief will be trampled on."
Rev Dr Matthew Roberts, Minister of Trinity Church York, warned that standard Christian teaching on sexuality and gender stands to be criminalised under the proposed ban.
"It is deeply concerning that the government seems to be considering legislation that would criminalise normal, loving Christian ministry, while stopping us from helping young people who are being caught up in the horrible damage being done by transgender ideology," he said.
"Nothing we do could be considered 'therapy'. But the proposals are drafted so badly, and with such apparent ignorance of basic Christian teaching, that entirely standard Christian teaching would be criminalised in the name of something that has nothing to do with us.
"'Conversion', as Christians understand it, is an amazing thing: realising that life is not all about focusing on ourselves, but on the God who made us. It is deeply wrong that this proposed legislation implies that being converted to Jesus Christ is akin to violence or abuse."
Rev Roberts also expressed concern about the rights of Christian parents to raise their children in accordance with their beliefs.
"Being able to raise children in their own faith is a legal right, and one which these proposals would take away. The government cannot do this without running into serious legal difficulties," he said.
"The Queen is appointed to be the Defender of the Faith. It would be very strange indeed if Her Majesty's Government legislated against the faith of their own sovereign."
Dr Julie Maxwell, a paediatrician and youth worker at St Mary's Basingstoke, said she was especially concerned about the potential impact of the proposed ban on pastoral youth work.
She warned that the ban would leave adults scared of sharing their views on gender and sexuality with young people.
"As we know children and young people need direction from adults around them regarding all sorts of lifestyle issues. Teenagers are navigating huge changes associated with puberty and issues around sexuality and gender are important topics that need to be discussed," she said.
"As Christians we seek to support young people who are seeking to follow Jesus Christ to understand these issues from the perspective of Biblical teaching regarding God's creation of men and women and his design for marriage.
"To find ourselves in a situation where parents, youth workers and other adults are afraid to address these issues risks leaving children and young people confused and vulnerable.
"There is already a significant increase in mental health problems in children and young people and being unable to support those struggling with issues around sexuality and gender identity will negatively impact on this."
Rev Graham Nicholls, Director of the Affinity church network, said he was prepared to go to prison to defend his traditional Christian beliefs.
He said: "We particularly wanted to write from the perspective of practitioners, people who are pastors, youth workers, and counsellors.
"We don't know how this law about conversion therapy could impact their work and their ordinary, everyday work of chatting with people, encouraging people, praying with people that could be severely impacted. So we thought it was important from the point of view of practising pastors.
"Those who are campaigning for the law, their stated aim is that prayers or any kind of encouragement to do what we would say the Bible is teaching in terms of sexual ethics, should be prohibited.
"We don't know how the law will work out, but I think if those demands were met, then really any conversation with your family or if your child asks a question about their sexuality or their gender and you give them some advice, potentially, that could fall foul of the law - if you give them advice from a Christian perspective that questions or suggests there is a good or a bad path to follow."
