The investigation is the first against a large social media platform under the Digital Services Act

The probe will focus in part on how X handles content that is illegal in Europe, including hate speech, disinformation and terrorist content related to the Israel-Gaza conflict. It will also examine the adequacy of the site’s “Community Notes” fact-checking system in Europe, X’s transparency mechanisms for advertisements and whether its revamped “blue check” verification system deceives users.

Margrethe Vestager, executive vice president of the European Commission, said such large online platforms pose a higher risk to society and, therefore, must abide by more specific standards.

“The higher the risk large platforms pose to our society, the more specific the requirements of the Digital Services Act are. We take any breach of our rules very seriously,” Vestager said in a statement.

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News of the investigation comes as X faces increasing scrutiny over the spread of disinformation related to the Israel-Gaza conflict. The Anti-Defamation League has reported that instances of antisemitic content have surged more than 900 percent since Hamas’s Oct. 7 attack on Israel. Musk also has faced criticism for using his own widely followed account to elevate antisemitic theories.

The E.U. action is the first formal proceeding against a large social media platform under the Digital Services Act, which came into force in November 2022. Under its rules, X could face fines of as much as 6 percent of its global revenue.

The investigation comes just weeks after European Commissioner Thierry Breton announced that the E.U. had issued the company a request for information on its handling of hate speech, violence and terrorist content. Breton also sent a warning letter to Musk directly, pressing him on whether the platform was being used to disseminate disinformation related to the Hamas attack.

“The #DSA is here to protect both freedom of expression & our democracies ― including in times of crisis,” Breton wrote on X in mid-October.

The law imposes special obligations on “very large online platforms and search engines,” which it defines as those used by at least 45 million Europeans each month. X qualified based on its declaration earlier this year that it has 112 million monthly users in Europe.

X chief executive Linda Yaccarino has said the company had removed or labeled tens of thousands of posts, while applying crowdsourced fact checks through a system called Community Notes. She also said the company assembled a group of leaders to handle crisis response to the war.

In June, Breton traveled to X’s San Francisco headquarters to oversee a “stress test” of its systems, including Community Notes, which was not yet available in all the languages of E.U. member nations. The European Commission has opened an office in downtown San Francisco as it expands its efforts to police the world’s largest online platforms, taking a tougher line against American tech giants than the U.S. government has.

Since buying Twitter in October 2022, Musk has loosened its policies governing what people can post and fired many of the people responsible for enforcing them. That has spooked advertisers and sent some users fleeing to rival platforms but has been welcomed by many conservatives in the United States.

The next steps in the E.U. investigation will include information requests that could involve interviews or inspections. The law does not set any formal deadline for bringing proceedings to an end, according to the Monday announcement.

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In response to the announcement, X’s safety division said the company is committed to complying with the Digital Services Act and is cooperating with the regulatory process.

“It is important that this process remains free of political influence and follows the law,” the company said. “X is focused on creating a safe and inclusive environment for all users on our platform, while protecting freedom of expression, and we will continue to work tirelessly towards this goal.”