"Facebook must answer these serious allegations and hold those responsible to account if there has been political bias in the dissemination of trending news," Senator John Thune, Chairman of Senate Committee on Commerce, Science and Transportation said after dispatching a strongly-worded letter to Facebook co-founder and CEO Zuckerberg yesterday.
"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?," Thune asked Zuckerberg.
In a statement responding to the allegations, Facebook claimed to have "rigorous guidelines in place for the review team" to prevent "the suppression of political perspectives" or the "prioritisation of one viewpoint over another or one news outlet over another".
"Please describe Facebook's organisational structure for the Trending Topics feature, and the steps for determining included topics. Who is ultimately responsible for approving its content?," Thune asked.
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Thune has also asked for a list of all news stories removed from or injected into the Trending Topics section since January 2014.
The White House, meanwhile, appreciated the clarification that came from Facebook in this regard.
"We were pleased to see the statement from Facebook making pretty clear that this was not something that they engaged in," White House Press Secretary Josh Earnest said.
"There is no denying that the kind of media environment that exists today places a special burden on consumers of news to make a concerted effort to seek out opinions that may differ from them. The nature of Facebook is that it helps people connect over large distances.