A top Republican in Washington wants Facebook to explain exactly how it chooses the news in its "trending" topics section.

The Commerce Committee, led by Republican John Thune of South Dakota, asked CEO Mark Zuckerberg to respond to anonymous allegations that former contractors suppressed news about conservatives and links to right-leaning websites. The controversy, first published by Gizmodo, is now trending on Facebook.

In a letter on Tuesday, Thune demanded to know who is ultimately responsible for approving stories for the "trending" box on the Facebook home page; what steps Facebook has taken to investigate the claims of bias; and how Facebook keeps records of its editorial decisions.

"Please provide a list of all news stories removed from or injected into the Trending Topics section since January 2014," Thune's letter said.

A Facebook spokesman confirmed that "we have received Sen. Thune's request for more information about how Trending Topics works, and look forward to addressing his questions."

It remains to be seen just how forthcoming Facebook will be. In its role as a quasi-journalistic publisher of information, the company may shirk at the prospect of handing over information about its editorial processes.

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"Facebook is free to reveal what information it chooses about its decision-making process and to defend its editorial process as it chooses," First Amendment attorney Floyd Abrams told CNNMoney. "Members of Congress and others may take issue with those decisions. But the First Amendment leaves no room for Congress to investigate or otherwise insert itself into Facebook's editorial decision-making."

While Facebook does not employ journalists who gather news, its News Feed is a powerful distributor of news stories from sources around the world. Teams of journalists and writers, known internally as "news curators," are in charge of managing the trending topics box.

Gizmodo's report on Monday said that "Facebook workers routinely suppressed news stories of interest to conservative readers from the social network's influential 'trending' news section, according to a former journalist who worked on the project."

Other anonymous former Facebook workers disputed the account. And there is no concrete evidence of systemic bias at Facebook. But it is possible that some individual workers may have rejected specific stories.

Related: Facebook needs more 'human bias'

"Trending Topics is designed to surface popular conversations — no matter where they fall on the political spectrum — and our guidelines require the review team members to allow all points of view," Facebook's Tuesday afternoon statement said.

Indeed, the trending box regularly includes news about conservative news sources.

"We have seen allegations that people did not honor the intent of those guidelines. Although the allegations are anonymous, we take them seriously. We are continuing to investigate whether any violations took place," the Facebook statement continued. "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."

Thune says he wants to know more about the operational practices.

"Social networks such as Facebook are an increasingly important source of news for many Americans and people around the world," he wrote. "Facebook has enormous influence on users' perceptions of current events, including political perspectives."

Thune asked the company to respond by May 24.