Warren, a leading Democratic 2020 candidate, has taken aim at the social media giant over its role in spreading disinformation against her and other candidates. Her campaign ran an ad on Facebook this past week that contained a deliberate lie to draw further attention to the issue.
That provocative move came after a recording leaked earlier this month of CEO Mark Zuckerberg telling employees that a Warren presidency would "suck" for the company.
Facebook fired back at Warren over the weekend via another social media platform, Twitter, where the company compared itself to broadcast television stations that ran the Trump ad and are regulated by the Federal Communications Commission.
The "FCC doesn't want broadcast companies censoring candidates' speech," Facebook said in a tweet. "We agree it's better to let voters -- not companies -- decide."
The comparison opened the door to additional scrutiny of Facebook's role in handling political speech. Facebook declined to comment for this story.
In response, Warren said the company's decision to compare itself to heavily regulated broadcasters raised even more questions about how it should be managed.
"You're making my point here," she tweeted. "It's up to you whether you take money to promote lies."
The episode underscores how Facebook is trying to maintain its position as a neutral platform even as it acquires ever more influence over public discourse and information -- and as it seeks to address weaknesses that made it a vehicle for Russian meddling in the 2016 presidential election.
Under current policy, Facebook exempts ads by politicians from third-party fact-checking -- a loophole, Warren says, that allows Zuckerberg to continue taking "gobs of money" from President Donald Trump's campaign despite Trump's ads telling untruths about former Vice President Joe Biden and his son, Hunter. Trump's efforts to pursue unfounded claims about the Bidens are at the heart of the burgeoning impeachment inquiry facing the President.
The Warren fight over ads highlights the collapsing distinction between traditional broadcast media and 21st-century digital platforms, experts say, raising fresh questions about how decades-old regulations concerning political speech should apply to massive online platforms that can influence millions of voters.
And according to some legal analysts, it exposes the limits of Facebook's arguments that it is not a media company.
Beginning with the Radio Act of 1927, Congress mandated that radio stations, and later TV stations, cannot pick and choose which political candidates' ads to run.
Broadcasters may choose not to air political ads at all, though that is rare in today's media environment and the law still requires them to carry ads by federal candidates, said Harold Feld, senior vice president at the technology think tank Public Knowledge. But broadcasters that do accept political ads must air all advertisements from qualified candidates, without a view toward their truthfulness or accuracy.
Broadcasters can still decline to air political ads from non-candidates, such as political action committees. And none of these rules apply to cable networks, which is why CNN could legally decline to air the Trump ad.
Facebook's comparison to broadcasters raises difficult questions about whether it is appropriate to import rules meant for TV and radio stations to the internet, Feld said.
"We face the same choices that we had when radio and television were the big gatekeepers," he said. "How much discretion do you want to give to these powerful shapers of public opinion while still being faithful to the principles of the First Amendment and letting the public decide?"
Broadcasters also obey a slew of other rules that companies such as Facebook do not, Feld said -- should Facebook have to comply with those as well?
For example, the government limits how many stations a media company may own in a particular market to limit anti-competitive behavior. Other FCC regulations require broadcasters to air a certain amount of children's programming, or to air sensitive content only after certain hours.
For a platform that targets content to users based on their interests and according to detailed data, reworking such rules for Facebook could be immensely complex and perhaps inadvisable, said Andrew Schwartzman, senior counselor to the Benton Foundation Institute for Broadband & Society, a civil society group.
"You can't apply that effectively, probably, to cable -- but certainly not to internet platforms," he said. "It's just impossible."
Facebook's reference to broadcasters also highlights a double standard. Schwartzman added that Facebook wants the benefit of the doubt afforded to regulated broadcasters, but "without the responsibility of being a regulated broadcaster."
Even those who have represented the broadcast industry say it is an odd and challenging position for Facebook to adopt.
"Facebook obviously doesn't want to be regulated like a broadcaster, so in a way it's strange they're citing this," said Jack Goodman, a former general counsel for the National Association of Broadcasters. "Because they're not regulated, and they certainly don't want to be regulated."
Warren's ads, which began running widely on Thursday, started with a bold but obvious falsehood: That Facebook and Zuckerberg had endorsed Trump's reelection campaign.
"You're probably shocked," read the ad, which reached tens of thousands of viewers nationwide. "And you might be thinking, 'how could this possibly be true?' Well, it's not."
On Saturday, Warren explained her ad was meant "to see just how far" the policy goes.
"We intentionally made a Facebook ad with false claims and submitted it to Facebook's ad platform to see if it'd be approved," she tweeted. "It got approved quickly."