WASHINGTON — A 30-second video ad that ran on Facebook this week falsely accused former Vice President Joseph R. Biden Jr. of blackmailing Ukrainian officials to stop an investigation of his son.
“Send Quid Pro Joe Biden into retirement,” a narrator in the ad intoned.
The video wasn’t released by the Trump campaign, which has produced ads on Facebook with similar accusations in recent weeks. Instead, it was made by an independent political action committee, or super PAC. And it was allowed to run on Facebook with false information, in violation of the social network’s policies on misinformation, the Biden presidential campaign wrote in a letter to Facebook on Thursday.
In the letter, which was viewed by The New York Times, the Biden campaign acknowledged that Facebook had a policy of allowing all political leaders’ speech and ads to remain up because the company considers them to be newsworthy. But the ad by the super PAC was not from a politician, the Biden campaign wrote, so it needed to be rejected.
“This is a most basic test,” Greg Schultz, Mr. Biden’s campaign manager, said in the letter. “The ad contains transparently false allegations, prominently debunked by every major media outlet in the country over recent weeks. It should be rejected.”
The letter exposed another vulnerability for Facebook as it struggles to tackle misinformation in the political ads that are flooding its site ahead of the 2020 presidential election. And it showed that Mr. Biden is escalating a battle against Facebook, blasting it in the letter for selling “the tools to target certain segments of the population with lies.”
The Biden campaign’s letter was delivered on the same day that Facebook’s chief executive, Mark Zuckerberg, delivered a vigorous defense of free expression in a speech in Washington. In the address, which drew strong rebukes from Democrats and civil rights leaders, Mr. Zuckerberg argued that even falsehoods from a politician were important for public discourse.
But Facebook had said that any other political ads could be submitted to fact-checking. The Biden campaign said that should have included the ad from the super PAC, the Committee to Defend the President.
In an emailed response to the Biden campaign on Friday, which was viewed by The Times, Facebook’s head of global campaigns, Katie Harbath, wrote that the ad was now inactive. If the ad ran again, she said, it would be submitted to fact-checking.
Facebook declined to comment further.
A week ago, an ad placed by the Trump campaign made similarly false corruption accusations about Mr. Biden. At the time, Mr. Biden’s campaign also sent Facebook a letter asking for the ad’s removal. Facebook refused, saying the ad was from a political leader and thus in the public interest.
That decision was criticized by the Biden campaign and Senator Elizabeth Warren, the Democrat from Massachusetts, who has promised to break up Facebook if elected president. Ms. Warren later posted a deliberately false ad on Facebook about Mr. Zuckerberg and Mr. Trump, daring the company to take it down.
The super PAC’s ad this week opened with a silhouette of Mr. Biden in front of an image of the White House. A narrator in a foreboding voice claimed the former vice president had blackmailed and threatened to withhold aid from Ukraine to stop an investigation into a company associated with his son Hunter.
Six versions of the ad were targeted to Facebook users in South Carolina, Iowa and Massachusetts, according to Facebook’s ad library. All versions are no longer active.
For years, Facebook has been assailed for unevenly enforcing its content policies across its family of apps, including Instagram, WhatsApp and Facebook Messenger. The company often reacted to problematic content that surfaced and made seemingly arbitrary decisions to reinstate or remove a given post.
In one of the best-known incidents, in 2016, moderators took down the Pulitzer Prize-winning image of Phan Thi Kim Phuc, the 8-year-old girl who was photographed fleeing napalm bombs during the Vietnam War. Because Ms. Phuc was naked, the image was removed from Facebook for reasons of child pornography. When Facebook was told about the news value of the image, it was allowed to remain.
Facebook does not permit certain types of material, such as pornography and posts that could incite violence, including hate speech and “dehumanizing” language.
The issue of what Facebook allows and does not allow on its site is unlikely to die down.
At a campaign event on Friday evening in Norfolk, Va., Ms. Warren took a couple of more shots at Mr. Zuckerberg. As she talked about breaking up big tech companies, she said, “Yes, Mark Zuckerberg, I’m looking at you.”
When Ms. Warren discussed a wealth tax in her speech, she again brought him up. “And Mark Zuckerberg, I’m still looking at you,” she said.
Cecilia Kang reported from Washington, and Mike Isaac from Boston. Thomas Kaplan contributed reporting from Norfolk, Va.