MENLO PARK (CBS SF / CNN) — Facebook removed — and then restored — an advertisement from Senator Elizabeth Warren’s campaign that sharply criticized Facebook and other tech companies for “tilting the playing field” in their favor.

Warren, a Democratic presidential candidate, wants to break up Facebook, Google and Amazon. She called them monopolies that abuse their dominant position in the marketplace.

The ad, part of a series posted by Warren’s presidential campaign, said the three tech companies have “bulldozed competition” and “used our private information for profit.” The ad’s removal was first reported by Politico.

In a statement, a Facebook spokesperson said the company originally removed the ad because it violated Facebook’s prohibition against modifying its corporate logo. The ad includes Facebook’s “f” trademark surrounded by a comic-book dialog bubble. It also includes icons to represent Amazon and Google.

Facebook said it restored the ad for the sake of “robust debate.”

It’s unclear whether the company’s artificial intelligence software or human content moderators took down the ad. Other Warren campaign ads on Facebook’s platform called for the breakup of Facebook and other big tech companies, but they did not include a modified Facebook logo. Facebook did not take those ads down. Facebook declined to comment on how the ad with the logo was removed.

Facebook polices millions of posts, videos, ads and other pieces of content each day with a combination of human and software intervention. It asks people to flag inappropriate content and Facebook hires contractors to moderate its platform. It also has developed software that automatically scrubs content it believes to have broken the company’s rules.

The AI software looks for telltale signs of misconduct, such as posts that include nudity, promote violence or violate copyrights. Facebook says it is also training AI to detect click-bait and misinformation. But AI remains in its infancy, and it is far from perfect. It cannot replace human judgment.

Facebook needs to use a combination of tools to combat its massive abuse problem on its platform. Human rights groups have slammed Facebook for its failure to crack down on hate speech and misinformation that fueled political division across the world, including violence in Myanmar. Facebook admitted it was “too slow” to act.

A year ago, Facebook publicized its community standards, detailing what it considers acceptable and unacceptable content for its platform. Facebook pledged to give people the ability to appeal decisions on reports filed on other people’s content.

Facebook taking down an ad criticizing its policies is perilous. It comes at a time when it faces blowback from politicians and customers around the world.

Political ads have been a sore spot for Facebook since the 2016 election, when Russian trolls with links to the Kremlin bought ads targeting Americans. They were able to do so without giving any information to Americans seeing those ads about who was paying for them.

On Monday evening, Warren cited the ad’s removal as evidence that the company has too much power.

“Thanks for restoring my posts,” she tweeted. “But I want a social media marketplace that isn’t dominated by a single censor.”

Warren’s far-reaching tech proposal would impose new rules on certain kinds of tech companies with $25 billion or more in annual revenue, forcing Amazon and Google to spin off parts of their companies and relinquish their overwhelming control over online commerce.

The plan also aims to unwind some of the highest profile mergers in the industry, like the combinations of Amazon and Whole Foods, and Google and DoubleClick, as well as Facebook’s acquisition of Instagram and WhatsApp.

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