The Napier Equippers Church may have to answer to the Advertising Standards Authority if the organisation deems its sign stating "Jesus Heals Cancer" falls within its jurisdiction.
The authority will also determine what codes the sign may breach, before reviewing complaints and allowing the church to respond.
It is investigating the Napier Equippers Church sign after receiving nine complaints.
The Tamatea church erected the billboard last week to the disgust of the local Condin family, whose three-year-old son is undergoing treatment for leukaemia. On Monday the church added a tally to the sign to symbolise the six people it claimed to have seen healed of cancer.
Advertising Standards Authority chief executive Hilary Souter said the complaints asked how appropriate the billboard message was.
"The chairman will look at the billboard and the complaints and make a decision whether it comes under our jurisdiction," she said. "It most likely is, we just need to confirm that."
The authority would take about 25 days to process the complaint.
Jody Condin, who initially submitted a complaint, said she was pleased the authority was investigating.
"I'd be happy if they at least looked into it, if they found that there was no wrong doing, [then] so be it."
Consumer NZ chief executive Sue Chetwin said from a consumer's position the billboard "falls between the cracks", as a church does not come under the Fair Trading Act.
But she was hesitant to advocate a type of control system, despite acknowledging the billboard could be hurtful.
"Do we want regulations for this sort of thing? A sensible person would probably ignore it."
The Ministry of Consumer Affairs also said the billboard did not fall under its jurisdiction as a church was not covered by the Fair Trading Act.
Senior Minister Lyle Penisular was not available today for comment.By Corey Charlton of Hawke's Bay Today