The authenticity of reviews on the TripAdvisor website is to be probed by the British Advertising Standards Authority (ASA).
A firm called KwikChex has suggested that as many as 10 million reviews on TripAdvisor could be fake.
TripAdvisor allows consumers to post reviews of hotels, holidays and restaurants and has 45 million visitors each month.
South African hoteliers have been concerned about the veracity of some of the reviews for some time and have told Hotel & Restaurant that they believe that malice lies behind some of them.
The editor of Hotel & Restaurant, Andrew Moth, says he is appalled by some of the drivel that masquerades as “constructive criticism” on sites like TripAdvisor and in blogs. “I always advise the victims that there is little point in wasting time fighting a battle that probably cannot be won.
Criticism is a fact of doing business but I have always found it astonishing that every Tom, Dick and Harry with a gripe thinks it right to broadcast it to the world. Unless it is justified – and some of the criticism is – ignore it. But it can be hugely damaging and the answer is to focus on the customers that you have and strive to get them to back again and again.”
Over the years South African restaurateurs and hoteliers have said there is simply no pleasing some people.
The British ASA said it would publish its findings "in due course".
An ASA spokesman told the BBC: "The Advertising Standards Authority has received a complaint from KwikChex about a claim on TripAdvisor's website.
"KwikChex has challenged whether the claims 'reviews you can trust', 'read reviews from real travellers', 'TripAdvisor offers trusted advice from real travellers' and 'more than 50 million honest travel reviews and opinions from real travellers around the world' are misleading and can be substantiated.
"They believe that TripAdvisor do not verify the reviews on their website and therefore cannot prove that the reviews are genuine or from real travellers," the ASA spokesman added.
The BBC said TripAdvisor declined to comment on the allegations or the ASA's forthcoming investigation. But Angus Struthers at TripAdvisor said it took the authenticity of customer reviews very seriously.
"We have numerous methods to ensure the legitimacy of the content on TripAdvisor," he said.
"We devote thousands of hours each year to battling fraud and improving our fraud detection efforts to ensure the integrity of our content," Struthers added.
However, Adam Raphael, editor of the Good Hotel Guide, told the BBC the ASA's inquiry was "long overdue".
"TripAdvisor is wide open to collusive and malicious reviews," he said.
Chris Emmins of KwikChex said he wanted an "impartial authority" to look at TripAdvisor's claims that its reviews were trustworthy.
"Instead of saying, 'These are reviews you can trust,' they need to put a disclaimer up saying they cannot say whether the reviews are verified or not," he said.