SAN FRANCISCO (AP) — 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 Democratic 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.

The Bloomberg posts weren’t much more than self-deprecating humor used to sell the 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.

Bloomberg’s 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.

Before the explosion of social media, it was 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.

Friday’s policy 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 doesn’t make money directly from such posts and doesn’t not consider them advertising.

As a result, branded content wasn’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.