With less than two weeks before the US presidential election, Facebook is failing to label who paid for some election ads, including some on behalf of Democratic nominee Joe Biden’s campaign.

As of Thursday morning, the Facebook page of Mitú, a news and entertainment website focused on Latino youth, had 11 active ads promoting Biden, none of which carried the payment disclosure required for election ads. The same page also had more than a dozen ads for the “Vote Like a Madre” election initiative, which also did not carry election ad disclosures and did not show up in Facebook’s election ads archive. The lack of disclosures was discovered by researchers at New York University.

Facebook requires advertisers of politics, elections, and social issues to register; it also mandates that their ads disclose who paid for them, how much was spent, and who was targeted. Those ads are indexed and stored in Facebook’s Ad Library for seven years.

Laura Edelson, a researcher with the NYU Online Political Ads Transparency Project, told BuzzFeed News that the Biden ads are what Facebook labels “paid partnerships,” more akin to sponsored posts with an influencer than a typical election ad.

“Those things have become a huge business right now, and they’re not made transparent in the Facebook Ads Library,” she said.

Mitú and Facebook did not immediately respond to requests for comment.

Along with Mitú’s ads, researchers found ads without proper disclosures from the Daily Wire, a right-wing site, Chinese state TV, as well as from pages for an insurance industry organization, a national LGBTQ advocacy group, and an anti-tobacco group in California. The Daily Wire ad promoted a story about Joe Biden with the headline “20 Lies & False Claims From the ‘Honest’ 2020 Candidate.”

Edelson and her team created a browser plug-in that has been installed by more than 6,500 people to collect ads about politics and issues on Facebook. Her team released a new “Missing Ads” page Thursday that shows how ads about the election and political issues are slipping through Facebook’s systems.

Facebook has attempted to show it can handle the 2020 presidential election after admitting that it had not done enough to prevent foreign interference in the 2016 election. Previously, the company said it would stop new election ads from being introduced in the week before voting day on Nov. 3, and that it would prohibit political and issue-based paid content in the US for at least a week after the polls close.

But Edelson and her colleagues previously found that Facebook failed to identify and label 9.7% of ads for elections and issues placed between May 2018 and June 2019. These undisclosed ads represented $37 million in spending. Edelson recently found that 8.6% of ads ran so far in 2020 without an initial disclosure.

“That is not necessarily a number to be proud of,” she said, pointing to Facebook’s impact and the number of ads that could be slipping through. “I happen to think the cost of undisclosed political ads is potentially really high.”

The Mitú ads supporting Biden started as early as Oct. 8 and appear to be part of a sponsored content deal with the Democratic presidential nominee’s campaign. Some of the ads directed people to sponsored articles on the Mitú website. Other ads sent them to voter registration pages maintained by the Democratic National Committee.

Edelson called Mitú “a really prolific political and nonpolitical advertiser” and said it’s concerning that Facebook was unable to consistently identify election ads coming from the page, as well as from other obvious political advertisers.

“We have seen lots of undisclosed ads from established political advertisers over the past couple of years, though, and I really don’t know why,” she said. “What I can say is that it appears to be the result of human error and that Facebook’s enforcement appears to be inconsistent. I have no way of quantifying how much of this is going on.”

A search of the election ad archive for Mitú’s page showed that Facebook previously removed ads that did not have the proper disclosures. Between October and June, Mitú ran hundreds of ads that the social network later deactivated.

“I commend Facebook for the degree of transparency that they are showing,” said Edelson, “but they have been pressured into it by the public because they’ve done things that are completely unreasonable.”

Without clearly communicated data, researchers and others can’t properly monitor and audit Facebook’s performance, Edelson said.

“I don’t think it’s reasonable to say that Facebook will catch every single last political ad,” she said. “But I do think that we should be able to answer the question: How good a job is Facebook doing? And right now, you can’t because you don’t have transparency of ads that Facebook has not labeled as political.”