An advertising agency based in Florida has filed a lawsuit against the social media company, alleging the new name infringes on its trademark of the letter X.

X Social Media, the plaintiff in the case, is an ad agency that focuses on mass-tort litigation. It claims in its suit to have been using X as its identity since 2016 and says it has a federal trademark covering that name. The company said it had spent over $400 million on advertising to build up the company’s name.

“Recent attempt[s by Musk] to register the [X] mark in association with social media, business data, promotion and advertising, business consulting, market research services, and advertising services…necessitates this action because its conduct has caused and will continue to cause serious irreparable harm to X Social Media,” the filing reads.

X Social Media further claims it has “already suffered loss in revenue that correlates with X Corp.’s rebrand and use of the mark ‘X.’”

This might be the first case against the company formerly known as Twitter over its new, preferred name, but it likely won’t be the last. Hundreds of companies hold trademarks covering the letter X, including Microsoft and Meta.

X Social Media is asking the U.S. District Court in the middle district of Florida to prevent Musk and his company from using the X name. It’s also requesting an unspecified amount in financial damages.

Musk has long been obsessed with the letter X, originally using it as the name for PayPal and even naming one of his children X. SpaceX incorporates the letter into its name. And, of course, Tesla’s Model X is one of four vehicles offered by the company.