A former Facebook employee has alleged that staffers tampered with the influential “Trending Topics” feed that highlights the most-discussed news stories across the social media giant’s global platform.

Remaining anonymous, the employee who claimed to have previously worked for Facebook’s “News Feed” section, told the tech website Gizmodo that staffers would often prevent stories with conservative topics such as the CPAC gathering, Mitt Romney, and Rand Paul, from “trending” as news stories on the site, and were more likely to include articles from CNN and the BBC than conservative sites like Breitbart, and Newsmax. The former employee also said that editors would insert other stories into the section whether or not they were actually the most read.

Facebook has denied that there is a corporate-sanctioned effort to impose a political agenda on its Trending Topics display.

“Depending on who was on shift, things would be blacklisted or trending,” the employee told Gizmodo. “I’d come on shift and I’d discover that CPAC or Mitt Romney or Glenn Beck or popular conservative topics wouldn’t be trending because either the curator didn’t recognize the news topic or it was like they had a bias against Ted Cruz.”

Facebook uses an algorithm to determine which topics are the most popular on the site, and their News team monitors these subjects. Before Trending Topics appear on the site, editors confirm the subject is tied to a current event, and then write a news description. Trending topics are personalized for individuals based on their interests and location, so they can often differ by user.

According to Facebook, no outlets are blocked from trending. A spokeswoman for the company told Variety: “We take allegations of bias very seriously. Facebook is a platform for people and perspectives from across the political spectrum. Trending Topics shows you the popular topics and hashtags that are being talked about on Facebook. There are rigorous guidelines in place for the review team to ensure consistency and neutrality. These guidelines do not permit the suppression of political perspectives. Nor do they permit the prioritization of one viewpoint over another or one news outlet over another. These guidelines do not prohibit any news outlet from appearing in Trending Topics.”

The allegations sparked much discussion Monday about the perception of bias within the world’s largest social media platform.