The Christian Institute has said it will take the government to court unless it ensures that the fundamental rights of parents and pastors are protected in a future ban on conversion therapy.
Women and equalities minister Kemi Badenoch has promised that the legislation will protect religious freedom and conversations about sexuality and gender identity with faith leaders, parents, teachers and counsellors.
Despite the assurances, concerns remain about the legislation and the lack of clarity around terminology.
Simon Calvert, Deputy Director of The Christian Institute, said that the banning of conversion therapy was "an absolute minefield, primarily because no-one knows what it is".
He said that activists were "profoundly intolerant" and that safeguarding was being weaponised in a bid to outlaw opposing views.
"Activists used to say they wanted to outlaw brutal abuse like electro-shock therapy. But that's already illegal," he said.
"Now they're admitting what they really want is to outlaw traditional theology and gender critical feminism. They are profoundly intolerant. They don't like the idea of churches praying prayers they don't agree with.
"They don't like women's activists and parents discouraging young people from rushing into gender transition."
Mr Calvert said that The Christian Institute was ready to take legal action if the government fails to protect freedom of speech and religion.
"Our solicitors wrote to the Westminster government preparing the ground for judicial review in May 2021," he said.
"If Parliament passes a law that tramples on basic freedoms of speech and religion we are ready to go to court to protect the fundamental right of parents and pastors to calmly explain their ethical beliefs without being prosecuted as abusers."