Hotels, restaurants and B&Bs are being held to ransom by TripAdvisor reviewers threatening to give disparaging reviews unless they are awarded free stays and meals.
Individuals are using blackmail to scam their way to better service and free upgrades, owners have said.
Martin Couchman, deputy chief executive of the British Hospitality Association (BHA), told MailOnline: "People threatening restaurants and hotels with bad TripAdvisor reviews to extort free things is a problem which has been growing.
“While it's very difficult to put an exact figure on how widespread the problem is, it is clear that small minority of online reviewers are directly blackmailing - or sometimes subtly blackmailing - restaurants for their own gain.”
He said that owners should not respond to such threats and should instead take their concerns to either TripAdvisor or the BHA.
A spokesman for TripAdvisor said: “Allegations of blackmail or threatening behaviour by guests against property owners are taken very seriously.
“If an owner experiences this, we urge them to contact us immediately. We have a way for owners to proactively report threats before a corresponding review is submitted.”