A report by technology news site Gizmodo said staff responsible for what was shown to Facebook's 1.6bn users frequently chose to bury articles they did not agree with.
Responding to the allegations, the network's head of search Tom Stocky wrote that the site "found no evidence that the anonymous allegations are true".
The claims come weeks after Facebook founder Mark Zuckerberg publicly denounced the policies of likely US presidential nominee, Donald Trump.
"I hear fearful voices calling for building walls and distancing people they label as 'others.'," the 31-year-old said at his firm's recent developers conference.
However, Facebook insisted Mr Zuckerberg's view did not influence what stories are given added visibility on the network.
The Trending Topics column appears in the top right corner of a typical Facebook page. It is designed to highlight what subjects are being discussed heavily by Facebook users around the world.
Facebook explained in a statement that this list was edited by humans so as to avoid regularly recurring popular topics - such as "lunch".
Facebook's Mr Stocky explained: "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."
The Gizmodo story, which quoted a person it said they had been one of the editors, alleged Facebook staff were routinely tampering with Trending Topic stories.
Gizmodo's source added that staff were told to seek out stories published on the BBC, CNN and other mainstream sites ahead of publications with a clearly stated political bias - even if the stories originated on those smaller outlets.
Also, if several mainstream media sites were covering the same story, Facebook would - according to the source - artificially place it in the Trending Topic column, even if it was not being discussed heavily by users.
Breitbart, one of the leading conservative news sources in the US, said the reports confirmed what they had "long suspected", that "Facebook's trending news artificially mutes conservatives and amplifies progressives".
The anonymous source also claimed that stories staff favoured - such as the Black Lives Matter movement - were given artificially greater prominence. Facebook said that this was "untrue".
After a day of growing reports across social media and in conservative-leaning publications, Facebook's Mr Stocky posted a response on his profile.
"We have in place strict guidelines for our trending topic reviewers as they audit topics surfaced algorithmically," he wrote.
"Reviewers are required to accept topics that reflect real world events, and are instructed to disregard junk or duplicate topics, hoaxes, or subjects with insufficient sources.
"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."
On Monday, Gizmodo's story about Facebook's Trending Topics section being biased was featured prominently in Facebook's Trending Topics section.
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Facebook has defended itself over claims its Trending Topics intentionally suppressed stories supporting conservative political viewpoints.