• Elon Musk lashed out at a media watchdog and unspecified large advertisers on Friday, as brands paused ad spending on X, the social network he owns and runs as CTO.
• Media Matters had published a report that found mainstream brands' ads running alongside pro-Nazi or other hateful user posts on X, formerly known as Twitter.
• Individually, Musk also caught a backlash after posting what the White House called "abhorrent promotion of antisemitic and racist hate" on X.

Elon Musk lashed out at large advertisers and Media Matters, a media watchdog group, on Friday after several major brands decided to pause spending on X, the social media platform he owns and runs as CTO.

Musk wrote late Friday night, "The split second court opens on Monday, X Corp will be filing a thermonuclear lawsuit against Media Matters and ALL those who colluded in this fraudulent attack on our company." He added, "Their board, their donors, their network of dark money, all of them..." and "the discovery and depositions will be glorious to behold," in subsequent tweets.

Media Matters for America (MMFA) published a report last week showing ads for mainstream brands on X, formerly Twitter, were running alongside user posts espousing pro-Nazi views. The report came after Musk personally posted a spate of tweets that the White House called an "abhorrent promotion of antisemitic and racist hate."

In response, advertisers including Apple, Comcast/NBC Universal (parent of CNBC.com), Disney, IBM, Lions Gate, Paramount Global, and Warner Bros. Discovery, then decided to halt their ad spending, at least temporarily, on the social media platform formerly known as Twitter.

Musk hawked a paid, ad-free subscription version of X in a tweet after news of suspended campaigns surfaced. He wrote, "Premium+ also has no ads in your timeline. Many of the largest advertisers are the greatest oppressors of your right to free speech." He did not specify which large advertisers he believes are "oppressors."

A spokesperson for X, Joe Benarroch, emailed a company blog post to CNBC that alleges Media Matters has "completely misrepresented the real user experience" of the social network.

He also said in the email: "Media Matters created an alternate X account and deliberately followed sensitive accounts to curate posts and get advertising to appear on the account's timeline to then misinform advertisers about the placement of their posts. These contrived experiences could be created on any social media platform."

Other social networks like Facebook, Reddit and TikTok, grapple with brand safety and moderation of hateful and false content on their platforms, too. However, Musk himself has drawn ire for personally boosting bigoted viewpoints in his own tweets, including in recent weeks, to his more than 163 million listed followers there.

In late October, an X user complained that a statue of Confederate general Robert E. Lee was melted down in Charlottesville, Virgina. The bronze was slated for use in new public art that would not glorify the losers of the Civil War. The user, who claimed to be a relative of the general lamented, "my kind is hated and many seek our extinction." Musk then replied in agreement: "They absolutely want your extinction."

Last week, Musk agreed with a post falsely claiming that the Jewish people have been pushing "dialectical hatred" against white people. Musk called the antisemitic post "the actual truth," prompting a backlash from brands, critics and even the White House.

The morning of Nov. 17, the White House admonished Musk saying he had engaged in an "abhorrent promotion of antisemitic and racist hate" which "runs against our core values as Americans."

Later on Friday, Musk declared a new policy for his social network: "As I said earlier this week, 'decolonization,' 'from the river to the sea' and similar euphemisms necessarily imply genocide. Clear calls for extreme violence are against our terms of service and will result in suspension."

The ADL's CEO Jonathan Greenblatt has praised Musk's promise to suspend accounts engaging in what he views as genocidal speech. Musk has been unwaveringly critical of the Anti-Defamation League, a Jewish-led organization that fights hate speech and discrimination. He also previously threatened to sue, but has not yet sued, the ADL.

It is not clear whether or when X Corp. will actually file a suit against Media Matters, or in which jurisdiction. X is based in San Francisco while the media watchdog is based in Washington, D.C.

Media Matters president Angelo Carusone said in a statement e-mailed to CNBC on Saturday:

"Far from the free speech advocate he claims to be, Musk is a bully who threatens meritless lawsuits in an attempt to silence reporting that he even confirmed is accurate. Musk admitted the ads at issue ran alongside the pro-Nazi content we identified. If he does sue us, we will win."

— CNBC's Jonathan Vanian contributed reporting