Vloggers have been given new advertising guidelines after concerns were raised that promotions were not being clearly marked.
The guidance from the Committee of Advertising Practice (CAP) encourages vloggers to make it clear when they are advertising a product.
It follows a ruling by the Advertising Standards Authority (ASA) last year which said vloggers paid to praise Oreo biscuits should have labelled the posts as adverts.
The new guidelines include product placement and "advertorial" vlogs where the content is controlled by the brand.
"If a vlogger is paid to promote a product or service and an advertiser controls the message then it becomes an ad," the CAP guidance says.
"When that happens, like all advertisers, vloggers must be upfront and clearly signpost that they’re advertising."
A list of eight scenarios where the advice might apply was published by the CAP.
The rules do not prevent vloggers from entering into commercial relationships. However, companies that request vloggers do not reveal they are advertising are potentially asking them to break the law, the CAP said.
Shahriar Coupal, director of the CAP, said: “Wherever ads appear we should be confident we can trust what an advertiser says; it’s simply not fair if we’re being advertised to and are not made aware of that fact.
"Our guidance will give vloggers greater confidence that they’re sticking to the rules which in turn will help maintain the relationship and trust they’ve built with their followers.”
Vlogging has become a highly profitable business, with the most successful earning their creators tens of thousands of pounds per month and potentially millions a year.