Top New Zealand golfer Michael Campbell is under attack for backing some controversial dietary supplements.
Michael Campbell has used Mannatech products for several years and endorses them in commercials.
But the Consumers Institute is disappointed he is supporting a company widely criticised for its products and marketing practices.
Mannatech sells $400 million worth of supplements a year - $20 million of that in New Zealand.
But the Medical Association says there is no scientific evidence to suggest Mannatech's products do any good.
The Ministry of Health issued warnings three years ago after claims from sales people that products like ambrotose could cure diseases like cancer.
MedSafe issued similar warnings to Mannatech last year, but the company stresses it does not make any therapeutic claims.
"We are in the wellness industry, not the sickness industry. We're not involved in curing, preventing, healing, mitigating disease in any way, shape or form," says George Howden from Mannatech Australia.
But Ian Mander has included the company in a website he manages, which lists various cults and religious groups.
"We're concerned that they're being marketed deceptively and the people are being taken for a ride when they buy the pills," says Mander.
Mannatech uses a multi-level marketing system with an army of 370,000 sales people worldwide.
It is also listed on the Nasdaq exchange. But some American investors are now suing Mannatech for allegedly inflating the company's shareprice by making false claims about miracle cures.
Head of the Consumer's Institute David Russell says the people involved are very enthusiastic for the sale.
"I would suggest that perhaps Michael Campbell should stick to playing golf, rather than advertising supposed nutritional supplements," says Russell.
Michael Campbell's agents don't believe he knows anything about the controversy.
"I don't think he's going to be willing to comment because I don't think... he's not a pharmacist or anything like that," says David Rollo of International Management Group.
But the Consumers Institute advises against using Mannatech's kids range of sugar coated gummy bears, which claim to have the nutritional goodness of 12 fruits and vegetables.
"We're not impressed at all, we believe the parents should persevere with real food rather than a supplement from a bottle," says Russell.