The US government has asked the EU’s General Court to let it join Elon Musk and X in their challenge to the €120 million fine Brussels imposed on the platform. The Justice Department announced the filing on Thursday.

The application covers two cases before the court in Luxembourg. One of the cases was brought by X Internet and X Holdings, and the other by Musk in his own name.

Both seek to cancel the Commission’s decision of 5 December 2025, the first fine issued under the Digital Services Act (DSA). The Commission found that X broke the law’s transparency rules through its paid blue checkmark, its advertising database and its limits on researchers’ access to public data.

X lodged its appeal in February. The fine applies to X and Musk jointly, and the Commission based it on the worldwide turnover of the businesses Musk controls, according to the Justice Department.

“The European Commission inappropriately attempted to expand its regulatory authority to reach American companies not present or operating within its jurisdiction,” said Brett Shumate, the assistant attorney general who runs the department’s civil division.

The department also objects to how the Commission decides who counts as the provider of a digital service. In its view, the decision reached Musk as a private person and other companies he owns that have nothing to do with X.

The State Department helped prepare the filing, as under Article 40 of the court’s statute, a state can take part in a case if it shows an interest in the result.

Washington has pushed back against the fine since it was issued. In December, the Office of the US Trade Representative threatened fees or restrictions on European service companies.

Weeks later, the State Department imposed sanctions on five people, including former EU commissioner Thierry Breton.

Brussels has since used the DSA again. In May, it fined the Chinese marketplace Temu €200 million over unsafe products, the second penalty under the law.

The General Court now has to decide whether to admit the US to the case. When X appealed, the Commission told AFP it was ready to defend its decision in court.