Facebook said it had erred in blocking a pro-Biden ad after initially reporting that the video violated its policy against "sensational" content.
A company spokesman cited an "enforcement error" and said Facebook was approving the ad, which showed clips of US President Donald Trump threatening to end Obamacare and Democratic presidential candidate Joe Biden saying "c'mon man" in response.
According to a screenshot of the rejection notice shared by Priorities USA strategist Josh Schwerin, Facebook had initially cited its policy against ads containing "shocking, sensational, inflammatory, or excessively violent content".
Examples of ad content barred by the policy include graphic depictions of torture, dehumanising speech and pimple popping.
Facebook has drawn heat for its relatively hands-off approach to political speech, particularly its policy of exempting politicians' posts from fact-checking.
It does maintain more stringent rules for outside groups like PACs, and earlier this month banned a Republican PAC from advertising after it repeatedly shared content that was deemed false by external fact-checkers.
Facebook also draws some lines for politicians, barring content that, for example, incites violence. In June, it removed Trump re-election campaign posts showing a red inverted triangle, a symbol used by the Nazis, for violating its policy against organised hate.
Facebook spokesman Andy Stone said only certain versions of the Priorities USA ad had been blocked, which he called "a mistake - an embarrassing one, actually," while other versions were allowed to run.
Priorities USA said the episode demonstrated the company's inconsistency in enforcing its rules.
"We've been trying to get these approved since Thursday. It should not take a public pressure campaign to get the company to follow its own policies," Schwerin said in a tweet.