The Christian Institute has launched a campaign in response to concerns that a ban on conversion therapy will "catch the ordinary work of churches".
The government has promised to ban conversion therapy, and plans to bring forward legislation after a public consultation.
Launching its Let Us Pray campaign today, The Christian Institute said that a broadly worded ban could hand LGBT campaigners "a veto on the ordinary work of churches".
The Christian Institute warns that Christian parenting as well as church teaching, pastoral care and prayer may all end up being criminalised.
At the heart of the campaign is the message that "praying shouldn't be a crime."
"Banning Christians from praying for their gay friends is oppressive and wrong," it said.
Christian Institute director Colin Hart said, "LGBT activists are pushing for a ban on any preaching, prayer and pastoral care that contradicts their theology.
"Private prayer, evangelism, parenting, pastoral advice, preaching and teaching, church membership, baptism, confirmation and communion would all be put at risk by an overly broad ban.
"These things, the ordinary work of churches, must not be criminalised.
"We want to protect gospel freedom. Politicians must not allow activists to exploit concerns about genuine abuse to further their own agendas against Christians."