Facebook decided Friday to allow a type of paid political message that had sidestepped many of the social network's rules governing political ads, in a reversal that highlights difficulties tech companies and regulators have in keeping up with the changing nature of paid political messages.

Its policy change comes days after presidential candidate Mike Bloomberg exploited a loophole to run humorous messages promoting his campaign on the accounts of popular Instagram personalities followed by millions of younger people.

It used to be clearer what's an ad and what isn't – and thus what's subject to disclosures and other rules. With social media, a campaign can pay celebrities and other influential users to spread a message on their behalf, without ever buying an ad and be subject to its rules.

"This is a new kind of activity that simply didn't exist when the rules for internet political communications were last updated," said Commissioner Ellen L. Weintraub of the Federal Election Commission.

The change involves what Facebook calls "branded content" – sponsored items posted by ordinary users who are typically paid by companies or organizations. Advertisers pay the influential users directly to post about their brand.

Facebook makes no money from such posts and does not consider them advertising. As a result, branded content isn't governed by Facebook's advertising policies, which require candidates and campaigns to verify their identity with a U.S. ID or mailing address and disclose how much they spent running each ad.

Until Friday, Facebook tried to deter campaigns from using such branded content by barring them from using a tool designed to help advertisers run such posts on Facebook and Instagram, which is owned by Facebook. Friday's rule change will now allow campaigns in the U.S. to use this tool, provided they've been authorized by Facebook to run political ads and disclose who paid for the sponsored posts.

"After hearing from multiple campaigns, we agree that there's a place for branded content in political discussion on our platforms," Facebook said in an exclusive statement to The Associated Press. "We're allowing U.S.-based political candidates to work with creators to run this content."

Politicians still won't be required to disclose how much it paid the influencers to run the posts.

The Bloomberg campaign had taken the unconventional step of paying social media influencers – individuals with huge followings – to post Bloomberg memes using their Instagram accounts. Different versions of the sponsored posts from the Bloomberg campaign ran on more than a dozen influential Instagram accounts, each of which have millions of followers.

That effort skirted many of the rules that tech companies have imposed on political ads to safeguard U.S. elections from malicious foreign and domestic interference and misinformation. Online political ads have been controversial, especially after it was revealed Russia used them in an attempt to influence the 2016 presidential election. In response, Facebook has rolled out a number of rules to prevent a repeat of that, though it has declined to fact-check political ads and refuses to ban even blatantly false messages.

The Bloomberg campaign's memes showed the candidate, in a tongue-in-cheek awkward fashion, chatting with popular social media influencers with names like "Tank Sinatra," asking them to help him raise his profile among younger folk.

With the sponsored posts, Bloomberg's campaign said it was reaching those who might not be normally interested in the day-to-day of politics.

"You want to engage people at every platform and you want them to feel like they're not just getting a canned generic statement," campaign spokeswoman Sabrina Singh said of the campaign's strategy.

The Bloomberg posts weren't much more than self-deprecating humor used to sell a candidate's old guy appeal, using a tactic that until now was largely used to sell skin care products or clothing-subscription services. But the lack of oversight and clear rules around influencer marketing, not to mention their effectiveness in reaching younger audiences, makes them ripe for misuse.

It's not yet clear if Facebook's sudden policy change will close all the loopholes, though the company says the issue represents a new territory and its approach could change over time. The same goes for regulation, too, which is even further behind than the tech companies.

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The Bloomberg campaign declined to say how much it paid for the sponsored posts, or if it had more of them in the works. The posts did not appear in Facebook's ad transparency library, which catalogs the political ads that campaigns buy directly from Facebook or Instagram, and tells users how much was spent on them. Mr. Bloomberg's campaign told the AP on Thursday that Instagram did not require the campaign to disclose that information on the sponsored posts it ran earlier this week. With Friday's change, the campaign would need to add the posts to the library, though it still wouldn't need to disclose spending amounts.

This story was reported by The Associated Press. Amanda Seitz reported from Chicago.