Sen. Elizabeth Warren and Rep. Alexandria Ocasio-Cortez tweeted their support Monday for Facebook employees who are challenging the firm's stance on lies in political ads.

According to an internal letter obtained by The New York Times on Monday, 250 Facebook employees are petitioning CEO Mark Zuckerberg to change the company's policy not to fact-check political advertising.

The two Democratic politicians made their views on the issue clear, with Warren describing Facebook's stance as "dangerous" and Ocasio-Cortez describing the Facebook employees as "courageous."

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Two US Democratic politicians have thrown their support behind the Facebook workers who are petitioning CEO Mark Zuckerberg to change the firm's policy on lies in political ads.

According to an internal letter obtained by The New York Times on Monday, 250 Facebook employees are petitioning Zuckerberg to change the company's divisive rules on political advertising that do not prohibit lying. In the letter, the employees say they "strongly object" to the policy and called on the firm to ban false political ads.

Sen. Elizabeth Warren of Massachusetts, who is a frontrunner for the 2020 Democratic presidential nomination, and Rep. Alexandria Ocasio-Cortez of New York, the freshman star of the Democratic left, separately tweeted about the issue Monday.

"Courageous workers at Facebook are now standing up to the corporation's leadership, challenging Zuckerberg's disturbing policy on allowing paid, targeted disinformation ads in the 2020 election," Ocasio-Cortez tweeted.

Warren's tweet a few hours later sharply criticized Facebook's policy and urged Zuckerberg to reverse his stance. "Facebook's own employees know just how dangerous their policy allowing politicians to lie in political ads will be for our democracy," she wrote. "Mark Zuckerberg should listen to them — and I applaud their brave efforts to hold their own company accountable."

Facebook's stance on political advertising has caused significant controversy in the run-up to the 2020 elections.

One particular source of controversy was a campaign ad for President Donald Trump that contained falsehoods about the Democratic frontrunner Joe Biden, which Facebook refused to take down.

To make her point, Warren also ran an ad on Facebook falsely suggesting Zuckerberg had endorsed Trump.

Rep. Alexandria Ocasio-Cortez has called Facebook's policy on lies in political ads "disturbing." MANDEL NGAN/AFP/Getty Images

Zuckerberg, though, has defended Facebook's stance while pointing to what he says are increased efforts from the company to fight the spread of misinformation on its site.

Ocasio-Cortez grilled Zuckerberg on the issue during a congressional hearing last week, asking Zuckerberg whether he saw "a potential problem here with a complete lack of fact-checking on political advertisements."

Though Zuckerberg said he disapproved of lying, he disagreed that it was Facebook's responsibility to fact-check all the content disseminated on its platform.

"Well, congresswoman, I think lying is bad, and I think if you were to run an ad that had a lie, that would be bad," he said. "That's different from it being in our position the right thing to do to prevent your constituents or people in an election from seeing that you had lied."

Despite his remarks, Facebook's stance on political lies appears inconsistent.

On Friday, Facebook blocked a PAC ad designed to test the social network's stance on political lies, a stunt akin to Warren's. The ad falsely claimed Republican Sen. Lindsey Graham of South Carolina had voted for Ocasio-Cortez's Green New Deal, something Graham is known to oppose. Facebook pulled the ad, suggesting that the social network might fact-check groups but not individual politicians.