MENLO PARK, CA — (CNN) An anonymous former Facebook contractor says he witnessed colleagues suppress news about “popular conservative topics” from the website’s “trending” section.

This allegation, published on Gizmodo Monday morning, ignited a debate over whether Facebook and other social media companies are prioritizing liberal viewpoints in their trending topics.

Facebook says it takes “allegations of bias very seriously.” What the former worker is describing, if it happened, would have violated the company’s “trending” guidelines.

“These guidelines do not permit the suppression of political perspectives,” according to a company statement. “Nor do they permit the prioritization of one viewpoint over another or one news outlet over another.”

Tom Stocky, who leads the Facebook team responsible for trending topics, said in a separate post that he has “found no evidence that the anonymous allegations are true.”

But the bottom line is that humans, unlike algorithms, have hearts. And the company can’t know for sure what was in the hearts of the workers who were selecting certain stories while rejecting others.

So the operators of many websites — some conservative-leaning and some not — are buzzing about the implications of Gizmodo’s report. By Monday afternoon, the topic was itself a trending story on Facebook.

The anonymous quotes in the report contributed to a long-held view among some prominent conservatives that Facebook, Twitter and other technology companies are infected by liberal bias.

Sean Davis, co-founder of the conservative web site The Federalist, tweeted about the alleged suppression, saying, “We’ve all experienced it.”

The Drudge Report led with the Gizmodo story on Monday afternoon, adapting Sheryl Sandberg’s book title “Lean In” to read “Leaning Left!”

In turn, some commenters dismissed those reactions as a “play the victim” strategy. In some ways, Monday’s debate mimicked a fight that’s been raging for decades about perceived liberal bias in news media coverage.

Meanwhile, others expressed skepticism. “We at RedState have certainly never observed any of the behavior that is alleged in the article being targeted at us, specifically,” wrote Leon Wolf, of the popular conservative site RedState.

Three former Facebook workers who spoke with CNNMoney echoed what some of Gizmodo’s other sources said — that personal biases might creep into the day-to-day “trending” work, but they never detected institutional bias for or against conservative information.

To the contrary, “the guidance from management was that it should be objectively representing what people are talking about, regardless of political views,” one of the sources told CNNMoney.

Another source, a former trending topic curator, said the teams prized transparency and open communication. While some stories that were trending across Facebook were blocked from appearing in the box, the intent was to weed out spam and other objectionable content.

“Blacklisted topics had to be logged by the team along with reasons,” the source said. “They were also checked… We were also very open with each other about the content we edited.”

A third source said, “no one ever told me to suppress a conservative story.”

The main source for Gizmodo’s story asserted that the tamping down of conservative stories happened more subtly, “depending on who was on shift.”

The source said, “I’d come on shift and I’d discover that CPAC or Mitt Romney or Glenn Beck or popular conservative topics wouldn’t be trending because either the curator didn’t recognize the news topic or it was like they had a bias against Ted Cruz.”

The person spoke on condition of anonymity, like CNNMoney’s sources did. Gizmodo quoted a second former contractor who said “it was absolutely bias” and “we were doing it subjectively.”

At issue is whether Facebook’s guidelines were violated by former contractors — and whether they’re still being violated today.

Jason Pontin, the editor in chief and publisher of MIT Technology Review, said Monday’s report came amid “a period of widespread paranoia amongst conservatives and Trump supporters that mainstream media, social media companies like Facebook and Twitter, and other elite institutions are routinely shadow blocking conservative opinions.”

He expressed doubt about any systemic suppression of conservative news by Facebook, citing CEO Mark Zuckerberg’s temperament.

While Zuckerberg seemed to criticize Donald Trump’s immigration rhetoric during the F8 conference last month, he is “acutely aware of the responsibilities and optics of becoming the global communications platform,” Pontin said. “Insofar as he’s an ideologue at all, he’s an ideologue for risk capitalism, the power of technology to achieve big things, and the benefits of openness and the social graph. He wouldn’t take this risk.”

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