The U.S. Senate Committee of Commerce has written a letter to Facebook founder and chief executive Mark Zuckerberg and asked him to appear in Washington to answer allegations that the social network suppresses certain political content trending among its users.

The letter, signed by Chairman John Thune, R-S.D., follows a Monday report by Gizmodo quoting several anonymous ex-Facebook employees who alleged the company's Trending Topics sidebar gives the news a liberal bent by "curating" certain topics over others.

"Have Facebook news curators in fact manipulated the content of the Trending Topics section, either by targeting news stories related to conservative views for exclusion or by injecting non-trending content?" the letter asks.

First reported by Gizmodo, the letter asks Zuckerberg to “arrange for your staff, including employees responsible for trending topics, to brief committee staff on this issue.”

'Vice President of Search Tom Stocky addressed the issue in a statement Tuesday morning, denying any political motives behind his team's curation and stating that Facebook's curators are held to guidelines that prohibit any kind of censorship.

Facebook confirmed receipt of the Senate letter but declined to comment further than the blog post.

The Senate committee's letter asks to see Facebook's guidelines, and requests "a list of all news stories removed from or injected into the Trending Topics section since January 2014."

"[H]ow many stories have curators excluded that represented conservative viewpoints or topics of interest to conservatives? How many stories did curators inject that were not, in fact, trending?" the letter asks.

The commitee includes Republicans such as Florida Sen. Marco Rubio and Texas Sen. Ted Cruz, who both ran for president, and Democrats such New Jersey Sen. Cory Booker.

Screenshots of the committee's letter are below:

US commerce letter Screenshot of the U.S. Commerce Committee's letter to Facebook CEO Mark Zuckerberg. Photo: IBT US commerce letter Screenshot of the U.S. Commerce Committee's letter to Facebook CEO Mark Zuckerberg. Photo: IBT

us commerce letter Screenshot of the letter from the U.S. Commerce Committee to Facebook CEO Mark Zuckerberg. Photo: IBT

commerce Screenshot of the U.S. Commerce Committee's letter to Facebook CEO Mark Zuckerberg. Photo: IBT