The Christian Institute has threatened to take legal action against the Scottish government if proposals to ban conversion therapy trample on religious freedom, parental rights and free speech.
The Scottish government is proposing a ban on "conversion practices" with prison sentences of up to seven years and the possibility of an unlimited fine for people convicted of breaching it.
A public consultation on the proposals closed on 2 April.
The Christian Institute said that the draft legislation contains only a "handful of vague criteria for what constitutes a conversion practice".
It fears that Christian pastors who preach traditional views and parents who try to stop their children from transitioning will fall foul of the ban.
Joanna Cook, a public affairs officer at The Christian Institute, said that the current draft was "vaguely worded, dangerously broad, and would catch innocent, harmless behaviour".
She gave the example of a mother who might try to stop her son from going to school wearing a dress and make-up. She said that under the terms of the current draft, this would meet the threshold of an offence being committed, risking prosecution.
"There are already strong laws on the statute book to protect gay and trans people. Existing law thankfully tackles verbal and physical abuse in Scotland today," she said.
"But those campaigning for a conversion practices law aren't content with that. They want a new speech crime, a thought crime. And, I'm afraid, the Scottish government's proposals give them that."
She said that plans to introduce pre-emptive "conversion practices protection orders", intended to stop 'conversion practices' from occurring in the first place, were "especially alarming".
"They would hand the courts very broad powers to restrict the free speech of individuals based purely on activists' speculation about what they might say to gay or trans people," she said.
Legal advice provided to The Christian Institute by human rights lawyer Aidan O'Neill KC warns that the proposed ban risks criminalising the ordinary work of churches and parents who want to protect their children from radical trans ideology.
Ms Cook added: "Our solicitors wrote to the government preparing the ground for judicial review in February 2022. If Parliament passes a law that tramples on basic freedom of speech and religion, we are ready to challenge it all the way to the Supreme Court if necessary."
