Facebook employees have been in contact with Sen. Elizabeth Warren’s presidential campaign regarding the candidate’s concerns with political ad policy, CEO Mark Zuckerberg told NBC Nightly News, and Bloomberg reported.

Zuckerberg has not spoken with Warren himself, and he did not elaborate on what exactly the staffers talk about. Facebook and the Warren campaign did not immediately respond to Business Insider’s request for comment.

Warren, a democratic candidate for president, has been vocally critical of Facebook. Breaking up big tech companies, including Facebook, is a key part of her campaign, and she has said that she would appoint regulators to undo anti-competitive mergers, such as Facebook’s ownership of WhatsApp and Instagram.

In leaked audio published by The Verge, Zuckerberg said that a Warren presidency would “suck” for Facebook.

Read more: Breaking up big tech was a big topic of discussion at the most recent Democratic debate - here's where all the candidates stand

Warren has also called out Facebook for running ads from the Trump campaign that made false claims about Joe Biden, another candidate. Facebook has had a "newsworthiness exemption" since 2016, meaning that it will leave up posts that violate community standards if "the public interest in seeing it outweighs the risk of harm." It also does not apply the same fact-checking standards to political ads.

Facebook tried to push back directly against Warren on Twitter, tagging her in a tweet, to which she responded: "You're making my point here. It's up to you whether you take money to promote lies."

Mark Zuckerberg reportedly already has ties to at least one candidate in the race. Zuckerberg and his wife, Priscilla Chan, have been recommending staffers to the Buttigieg campaign, Bloomberg reported. Two of the staffers have been hired by the campaign.

A spokesperson for the Zuckerberg-Chans told Bloomberg that the couple had not decided who to support for president.