Sen. John Thune (R-S.D.) has asked Facebook CEO Mark Zuckerberg to respond to anonymous allegations made in a story published by Gizmodo that the company suppressed conservative news on its website.

According to CNN, Thune, who heads the Senate Commerce Committee, sent a letter on Tuesday requesting information on who is in charge of the stories that appear in the website’s “trending” news box; how Facebook has looked into charges of bias; and how Facebook tracks these editorial choices.

Tom Stocky, an executive who is in charge of the Facebook team responsible for “trending” topics, said in a post Monday night that the company had investigated these allegations, and did not find any wrongdoing by employees.

“Trending Topics is designed to showcase the current conversation happening on Facebook. Popular topics are first surfaced by an algorithm, then audited by review team members to confirm that the topics are in fact trending news in the real world and not, for example, similar-sounding topics or misnomers,” Stocky wrote.

He added that the technology that Facebook uses does not allow editors to cherry-pick news outlets:  “Facebook does not allow or advise our reviewers to systematically discriminate against sources of any ideological origin and we’ve designed our tools to make that technically not feasible. At the same time, our reviewers’ actions are logged and reviewed, and violating our guidelines is a fireable offense,” Stocky wrote.

Gawker Media, the company that publishes Gizmodo, told the Wall Street Journal it stands by the story.

“We are proud of Mike Nunez’s thorough and ongoing reporting into the opaque process by which Facebook decides what news its users see,” said John Cook, editor in chief of Gawker Media, in a statement. “The immediate and intense response to our accurate story shows why an independent media is critically important for keeping powerful companies like Facebook accountable.”