YouTube is under mounting criticism from conservatives who claim a “Restricted Mode” feature on the site—which is intended to hide graphic content—is censoring videos about topics like Israel and university diversity.

The controversy erupted after a YouTube GOOG channel called PragerU, which offers dozens of lectures with a conservative slant, launched a petition asking YouTube to remove the “restricted” tag from videos like “Who’s More Pro-Choice: Europe or America?” and law professor Alan Dershowitz’s “Israel’s Legal Founding.”

The “restricted” setting, which users can see at the bottom of a YouTube page, does not cause a video to disappear from the site entirely but instead serves as a filter for those who activate the setting. It’s typically used by parents who want to prevent their children from seeing offensive content, but also by schools and public libraries — which boost the claims of those who say the setting can serve to censor political views.

A search for “Israel” or “feminism,” for instance, results in certain YouTube videos not appearing at all when “Restricted Mode” is on. Meanwhile, clicking on a link to a “restricted” video—such as this one called “Are Men Obsolete” by a scholar at the American Enterprise Institute—will result in a YouTube user seeing a screen like this if the filter is on:

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YouTube won’t disclose precisely what triggers its algorithms to designate certain videos as “restricted,” but the company did acknowledge that one of the factors is “community flagging.” This led the Wall Street Journal to warn that this power to flag videos could trigger a swarm of censorship by activists:

“Yet it’s easy to imagine a flood of users reporting a political video—microagressed [sic] college students have a lot of free time—and limiting a viewpoint’s audience,” said the paper in an editorial this week.

The “restricted” feature is also problematic because YouTube doesn’t offer a way for the owners of videos that receive the label, such as PragerU, to challenge the designation.

In response to questions from Fortune about why YouTube is restricting certain videos based on what appears to be political views, rather than violence or pornography, a spokesperson provided the following statement:

Restricted Mode in YouTube is an optional feature used by a small subset of users to filter videos that include sensitive content. It’s based on algorithms that look at a number of factors, including community flagging on videos. As with many of our products, our goal is to improve it over time based on community feedback and we encourage users to flag videos they feel should be included on Restricted Mode.

It’s unclear how many other videos that appear to be political in nature have been restricted under YouTube’s system.

YouTube is a private entity under the larger Alphabet umbrella, so it has no legal obligation to change its restrictions setting—or even to publish anyone’s video in the first place. But the flap over the videos, which was also picked up by the Boston Globe, underscores a larger controversy over how companies like Google, Twitter TWTR , and Facebook FB should address their roles as major media outlets where people come to obtain news and information.

Last month, for instance, Facebook sparked outrage when the company blocked a newspaper and others users from publishing an iconic Vietnam War photograph showing a naked child screaming in pain from a napalm attack. The social network has also repeatedly landed in hot water over its “trending stories” section, which has promoted partisan news or outright conspiracy theories.

The petition asking YouTube to restore the restricted UPrager videos had reached about 70,000 names by midday Friday.