As Mark Zuckerberg prepares to testify on Capitol Hill, the question on most lawmakers’ minds will be the company’s abuse of data privacy. But there’s another issue of growing concern to voters — Facebook’s new determination to manipulate the flow of news and political information to its users.

Facebook now admits that it is behaving more like a publisher, with an editorial view, than a neutral platform where users get to choose what they read. Its head of news partnerships has said that Facebook now has a “point of view” on the news, while Zuckerberg himself says that Facebook, not its users, will now determine what counts as a “quality” news source.

Facebook would like to convince the public that they aren’t taking any sides, that a news source can be “quality” whether it’s aligned with the left or the right. But the results of Facebook’s new approach can already be seen, and show that the platform has indeed taken sides. They’ve taken the side of the establishment against the anti-establishment – and especially Donald Trump.

The beneficiaries of Facebook’s recent changes to its newsfeed are a sea of old-world media: CNN, NBC, ABC, The Washington Post, and The New York Times have either been unaffected by Facebook’s changes or have seen their traffic rise.

A report by the social media analytics company NewsWhip found that corporate media outlets, most notably CNN, saw average engagement on their posts soar upwards by almost 50 percent this month. Non-corporate right-wing media, including Breitbart News, saw their engagement fall. Breitbart News slid from the 9th most-engaged site on Facebook in December to 21st in March, while Western Journal fell from 12th in February to 22nd in March.

The losers are not just the right, but the whole anti-establishment media. Conservative new media has been hit hard, true: Gateway Pundit has taken a massive hit on both Facebook traffic and engagement, as has Breitbart and PragerU. But so too has ShareBlue and BuzzFeed. Talking Points Memo, another website of the populist left, has seen its Facebook traffic drop by nearly 80 percent.

Facebook is propping up old media at the expense of new media, elites against populists, and establishment against anti-establishment. Zuckerberg claims to simply be opposing “partisanship” and “fake news” — in reality he has taken a partisan position, on the side of elites against populists of both the left and right.

Two sites, the conservative publication Rare.us and the viral news site LittleThings, were hit so badly that they have had to lay off their employees and shut down. After giving new media the impression they could be successful on Facebook if they built up enough fans, Facebook has, suddenly and without warning, snatched away their livelihood.

News sites will now have to spend time adjusting their content to Facebook’s new rules, again highlighting the company’s new role as de facto editors of the world. And Facebook still has the power to change their algorithm suddenly and without warning, throwing yet more news organization into turmoil. Even if news sites dance to Zuckerberg’s tune, it could all still be taken away in an instant, as it was for Rare and LittleThings.

The senators and members of Congress who question Zuckerberg this week are bound to be concerned by Facebook’s abuse of user data. But they should also ask why one company is allowed to set the rules for the entire industry of journalism – and adjust them at a moment’s notice to favor one faction or another.

It is not as if news publications can go elsewhere. Facebook, with 2 billion users, has no serious competitor in social media. Other methods of distributing news on the internet are inferior, rapidly declining, or else controlled by one of the other tech giants, whose track record of arbitrary rule-changes is as bad as Facebook’s.

Unless Congress believes that every news publication in America should be at the mercy of a few unaccountable executives in Silicon Valley, they must question Mark Zuckerberg on this issue too.

Allum Bokhari is the senior technology correspondent at Breitbart News. You can follow him on Twitter, Gab.ai and add him on Facebook. Email tips and suggestions to allumbokhari@protonmail.com.