Warren lodged her latest attack after Zuckerberg gave a speech on free expression . In his speech at Georgetown University, Zuckerberg defended his decision to err on the side of allowing more speech on Facebook, rather than less, even as the company has been attacked by both political parties for the types of content it hosts. Facebook has been criticized for both what it does and does not fact-check on its platform, and conservatives have complained that Facebook suppresses their voices.

"Facebook is actively helping Trump spread lies and misinformation," the senator from Massachusetts said in a tweet Thursday, adding that Facebook is "unprepared" to deal with the 2020 election.

Democratic presidential hopeful Elizabeth Warren took another jab at Mark Zuckerberg, accusing the Facebook CEO of helping Donald Trump win the presidential election in 2016 and aiding his reelection at a profit.

Political ads have been a sticking point for Facebook in the past few weeks after the company said it will not remove or fact-check false ads placed by politicians in a response to a request from Joe Biden's presidential campaign to remove an ad with unsubstantiated claims placed by Trump. Zuckerberg said in the speech that he's gone as far as to consider eliminating political ads, but said it would still leave ambiguity on where to draw the line.

"There are many more ads about issues than there ads about elections. Do we ban ads about health care, immigration or women's empowerment?" he asked. "If you're not going to ban those, does it really make sense to give everyone else a voice in political debates except for the candidates themselves?"

Warren previously attacked the policy and deliberately placed her own ad falsely claiming Zuckerberg endorsed Trump to test how far Facebook would take its own rules. In response, a Facebook spokesperson previously told CNBC, "If Senator Warren wants to say things she knows to be untrue, we believe Facebook should not be in the position of censoring that speech."

Facebook did not immediately respond to a request for comment on Warren's latest tweets.

Publicly, Zuckerberg has appeared mostly unflappable in the face of Warren's calls to break up his company. But there's now evidence that he does see her campaign as a threat, after a leaked recording of his meeting with employees heard him acknowledge that Facebook would likely face "a legal challenge" under her administration, though he said he'd bet Facebook would win.

In the past week, Warren took another step to distance herself from the tech giants by pledging to turn down contributions over $200 from Big Tech executives. She also swore off large donations from executives at big banks, private equity firms or hedge funds after previously promising to deny the same from pharmaceutical and fossil fuel executives.

Subscribe to CNBC on YouTube.

WATCH: How Facebook makes money by targeting ads directly to you