“Rather than seeing progress, we have seen regression,” Biden’s campaign said in a letter to Zuckerberg on Monday. “Facebook’s continued promise of future action is serving as nothing more than an excuse for inaction.”

The letter, obtained by Fortune, suggests that Facebook has failed to live up to its own policies and promises to protect against election disinformation. It refers to posts from President Trump and his son Donald Trump Jr. that encouraged people to vote by mail and in person and suggested that people opposed to Trump plan to submit “millions of fraudulent ballots.” 

In response to the letter, a Facebook spokesperson provided the following statement: “While many Republicans think we should take one course, many Democrats think we should do the exact opposite. We’ve faced criticism from Republicans for being biased against conservatives and Democrats for not taking more steps to restrict the exact same content. We have rules in place to protect the integrity of the election and free expression, and we will continue to apply them impartially.”

The letter from Biden’s campaign was sent just one day before Biden faces off against Trump in the first 2020 presidential debate. It also comes during a contentious election year, when, owing to the coronavirus, many voters will vote by mail and election results may not be final until well after the election.

Meanwhile, Facebook, under fire for allowing misinformation and fake news to spread during the 2016 presidential election, has promised to do better this time around. It has said it would remove posts that provide misinformation about voting and that it wouldn’t accept new political ads within a week of the election.

But Biden’s camp isn’t convinced.

“Mr. Trump and his allies are hijacking this model to sow distrust in our democracy,” Monday’s letter reads. “You have committed not to allow that to happen. Yet you do allow it to happen—time and again.”

This is the second time the Biden campaign has taken aim at Facebook. Earlier this year, the former Vice President demanded that Facebook do more to prevent the spread of misinformation and “rants of bad actors and conspiracy theorists.” In a letter to Zuckerberg, he asked Facebook to stop allowing political groups to lie in ads—those are currently allowed—and asked that the company promote news from credible sources and block voter suppression efforts by anyone, including President Trump.

In Monday’s letter, signed by Biden campaign manager Jen O’Malley Dillon, the campaign argued Facebook works against its “founding principle” to empower individual voices and rather “caters to those who already have power.” The campaign also says it plans to call out Facebook’s failures as they occur leading up to the election.