Facebook founder and CEO Mark Zuckerberg. Chesnot | Getty Images

In a letter to Joe Biden's presidential campaign, Facebook doubled down on its policy to allow speech from politicians to go unchecked regardless of the truthfulness of their claims. Facebook's Letter to Biden Campaign (Tweet) The letter, originally obtained by The New York Times, was a response to the Biden campaign's request for Facebook to reject or demote ads from President Donald Trump's reelection campaign that have not been backed by evidence. The Biden campaign's original request to Facebook, addressed to CEO Mark Zuckerberg, COO Sheryl Sandberg and global elections policy chief Katie Harbath, pointed to an ad by the Trump campaign that contains a statement that has not been proven by evidence that the former vice president "offered Ukraine $1 billion to fire the prosecutor investigating a company affiliated with his son." Biden Campaign's Letter to Facebook (Tweet) "The allegation of corrupt motive has been demonstrated to be completely false," the Biden campaign wrote, according to a copy of the letter posted online by a CNN reporter. The campaign said the claim should be covered by Facebook's pledge to reject political ads with "previously debunked content."

CNN had refused to air the ad, with a spokesperson telling NBC News last week, that "it does not meet our advertising standards," and that "the ad makes assertions that have been proven demonstrably false by various news outlets." Other tech companies like Twitter and Google's YouTube are running the Trump ad. Trump's campaign spent more than $1 million on Facebook ads in one week as it ramped up messaging against the House's impeachment inquiry into the president, ABC News reported. In its response to the Biden campaign, according to the copy of the letter also posted by the CNN reporter, Facebook reiterated its recently stated policy of taking a hands-off approach to speech by politicians. "Our approach is grounded in Facebook's fundamental belief in free expression, respect for the democratic process, and the belief that, in mature democracies with a free press, political speech is already arguably the most scrutinized speech there is," Harbath wrote. "Thus, when a politician speaks or makes an ad, we do not send it to third party fact checkers." Harbath said the company would take steps to reduce the reach of a "viral hoax" shared by a politician, however. "That is different from a politician's own claim or statement — even if the substance of that claim has been debunked elsewhere," Harbath wrote. "If the claim is made directly by a politician on their Page, in an ad or on their website, it is considered direct speech and ineligible for our third-party fact checking program."