SAN FRANCISCO (CNN) — Reddit has warned users of its forum for President Trump supporters that “systematic harassment” of the alleged potential whistleblower whose complaint kicked off the impeachment inquiry “must stop immediately.” The company, headquartered in San Francisco, cited in part its policy prohibiting “inviting vigilantism.”

The Reddit forum, known as “The_Donald” subreddit, has previously been embraced by Trump and his inner circle.

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In a message to the Trump supporters that run the forum that was posted Tuesday, Reddit staff said, “posts that do nothing more than attempt to focus mob attention on this alleged individual cross a line.” The company said it had seen a “dramatic rise” in these types of posts in recent days.

“Please note that our rules about harassment and our prohibitions on inviting vigilantism still apply to any discussions speculating about the whistleblower’s identity,” they added.

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In response, users of the forum have promoted alternative sites to continue communicating in case Reddit shuts The_Donald down.

In 2016, then candidate Trump held an “ask me anything” session on the forum. The_Donald subreddit plays a central role in the online Trump-supporting world, with topics and memes often going viral there before they trend on Twitter, Facebook, and other platforms. Trump himself has tweeted at least one meme made by a user of The_Donald and Trump’s current campaign manager said in 2016 that he visits it every day.

In June, Reddit put some restrictions on the forum because of what it said were “threats of violence against police and public officials.”

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Facebook and YouTube said two weeks ago that they were removing mentions of the potential name of the alleged whistleblower. However, CNN has since found mentions of the individual on both sites.

“We do not have a specific policy around whistleblowers,” a Reddit spokesperson said in a statement to CNN on Wednesday. “Our policy encourages an open discussion regarding issues of public and political relevance, however it forbids posting of personal information, or the encouragement of harassment or vigilantism. Context is important in these matters and we have and will continue to action posts and users that are in violation.”

During a discussion hosted on Reddit in June, Senator Ron Wyden, a Democrat, asked Reddit CEO Steve Huffman what the company was doing about moderating content on The_Donald.

“From what I am told, The_Donald is home to messages that cross the line toward inciting the hatred that is eroding our democracy,” Wyden wrote.

“As it relates to r/the_donald specifically,” Huffman replied, “we watch them closely, and we do our best to hold them to the same standards and policies as we do all communities. Before we action any community.”

Huffman then explained why he’s not generally in favor of banning a group like The_Donald, saying, “banning a large political community that isn’t in violation of our policies would be hugely problematic, not just for Reddit, but for our democracy generally. Political speech is the most protected form of speech in the United States, and we are sensitive to that and take cues from the government when we think about our policies.”

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