The Advertising Standards Authority (ASA) has stepped in after a Nottingham church claimed in a leaflet God could heal a range of named illnesses.
It followed a complaint from the head of Nottingham's Secular Society who was handed a flyer while shopping.
The leaflet, distributed by St Mark's Church in Woodthorpe, said God could heal back pain and cancer.
The ASA said "robust evidence" was needed to support such claims.
Matt Wilson from the ASA said: "We are not here to stop religious or faith-based organisations from promoting what they believe in.
"But if they are making absolute claims about curing serious conditions then we have to see that evidence to back it up."
Dennis Penaluna of Nottingham Secular Society said he was shocked by the leaflet.
"I couldn't believe the overarching, ridiculous, unfounded claims they were making. They can't be substantiated," he said.
"It's a dangerous nonsense. People who are ill or vulnerable can be easily persuaded. They will grasp at anything."
Canon Ed Pruin, who advises people in the Church of England diocese of Nottingham and Southwell on healing, said he agreed the leaflet was "less than helpful".
But he added: "I absolutely do believe that God can heal. I have no doubts.
"I think that one of the ways God heals is through medical science and the care of healthcare professionals.
"But I don't think that he is always in the curing business."
Canon Pruin is on the Healing and Wholeness committee that advised St Mark's to amend the leaflet in accordance with the ASA recommendations.
"The words 'healing on the streets' is perhaps a little misleading. I personally would like to see 'care on the streets'.
"People want to be prayed for when they are sick. We are responding to a need," he said.
No-one from St Mark's Church was available for comment.
Members of the church have been part of the Healing On The Streets ministry for two and a half years.
The Healing On The Streets ministry was started by Causeway Coast Vineyard church in Coleraine, Northern Ireland, in 2005 and has been taken up by dozens of churches across the UK.
Other churches in the ministry have said they would now look at their leaflets to make sure that they are not able to be misinterpreted or misunderstood.