The Senate Committee on Commerce, Science and Transportation asked Facebook Chairman and Chief Executive Mark Zuckerberg in a letter to answer questions about the company's news curation practices and its trending topics section.
The investigation comes after Gizmodo reported on Monday that a former Facebook employee claimed workers "routinely suppressed news stories of interest to conservative readers," while "artificially" adding other stories to the trending list.
US Senator John Thune, the chairman of the committee, told reporters Tuesday his primary concern was that Facebook may be engaging in deceptive behaviour if employees meddled with what trending news was displayed.
"If you have a stated policy, which your followers or your audience knows to be the case, that you use an objective algorithm for trending topics you better follow that policy," Thune said. "It's a matter of transparency and honesty and there shouldn't be any attempt to mislead the American public."
The letter to Facebook includes requests for information on the organizational structure for the "Trending Topics feature."
Adam Jentleson, deputy chief of staff to Democratic Senator Harry Reid, balked at the request in a statement provided to Reuters.
"The Republican Senate refuses to hold hearings on [Supreme Court nominee] Judge [Merrick] Garland, refuses to fund the president's request for Zika aid and takes the most days off of any Senate since 1956, but thinks Facebook hearings are a matter of urgent national interest," Jentleson said.
A Facebook spokesman said it had received Thune's request for more information about how "Trending Topics" works.
"As we investigate, we will also keep reviewing our operational practices around Trending Topics - and if we find they are inadequate, we will take immediate steps to fix them," the spokesperson said.
Tom Stocky, the vice president of search at Facebook, responded to the allegations Monday night in a lengthy post published to the social media site saying there are "strict guidelines" for trending topic reviewers who "are required to accept topics that reflect real world events."
He added that those guidelines are under "constant review" and that his team would "continue to look for improvements."
Katie Drummond, the editor-in-chief of Gizmodo, called her publication's story "accurate" in a statement released to Reuters Tuesday.
Gizmodo's report alarmed several social media users, with some conservatives in particular criticizing Facebook for alleged bias.
"'If a Conservative Speaks - and Facebook Censors Him - Does He Make a Sound?'" Wisconsin Governor Scott Walker (@ScottWalker) wrote on Twitter on Tuesday, with a link to a National Review story that detailed the allegations against Facebook.
© Thomson Reuters 2016
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