US market regulators on Wednesday went to court to stop Meta from buying virtual reality fitness app maker Within, a potential blow to the tech giant's metaverse ambitions.

In a complaint filed in federal court, the Federal Trade Commission argued that Facebook-parent Meta is trying to illegally expand its virtual reality empire with the buy of Within Unlimited, maker of fitness app "Supernatural."

Meta has made it a focus to build its metaverse vision for the internet's future, betting heavily on the interactive virtual world that the company believes will keep it relevant.

"Instead of competing on the merits, Meta is trying to buy its way to the top," FTC competition bureau deputy director John Newman said in a release.

"This is an illegal acquisition, and we will pursue all appropriate relief."

Meta did not immediately respond to a request for comment.

Meta is already a leading player in the virtual reality market, and its chief Mark Zuckerberg has stressed that the metaverse is key to the company's future.

The Silicon Valley titan years back bought virtual reality gear maker Oculus and studios devoted to apps for use in digital realms.

Meta purchases have included a popular "Beat Saber" game in which players slash at oncoming virtual blocks in time to music.

The FTC said that the suit seeks specifically to block Meta and Zuckerberg from getting their hands on Within Unlimited.

The Supernatural app made buy independent studio Within lets users work out in routines set to music by popular artists such as Lady Gaga, Katy Perry, and Coldplay in realistic, virtual locales such as the Galapagos Islands, the FTC said.

The complaint quoted Within's as calling fitness apps "the killer use case for VR."

"Meta is a potential entrant in the virtual reality dedicated fitness app market with the required resources and a reasonable probability of building its own virtual reality app to compete in the space," the FTC said in the complaint.

"But instead of entering, it chose to try buying Supernatural."