The likes of Ellie Goulding, Rita Ora and Rosie Huntington-Whiteley are among 16 stars who have pledged to make the change - which will mean that going forwards, they will clearly state whether they have been paid or received any gifts for the products they're endorsing.
The move follows warnings from the Competition and Markets Authority (CMA), which suggested that certain posts could be breaking the law.
Andrea Coscelli, the chief executive of the CMA, explained: "Influencers can have a huge impact on what their fans decide to buy. People could, quite rightly, feel misled if what they thought was a recommendation from someone they admired turns out to be a marketing ploy.
"You should be able to tell as soon as you look at a post if there is some form of payment or reward involved, so you can decide whether something is really worth spending your hard-earned money on."
Meanwhile, Geraint Lloyd-Taylor, legal director at the law firm Lewis Silkin, admitted that in the UK, the rules are quite difficult to stick to.
He told the BBC: "The CMA has portrayed these posts as if some celebrities are deliberately trying to pull the wool over the eyes of their fans, but often it is just that the various guidance is difficult to follow.
"I think the hashtag #ad will become the default, but it seems that the CMA intends to also look more at what the platforms are doing and it might be that we see more built-in tools and other changes from them as well."