BTS, the world's biggest K-pop group, is facing a copyright infringement lawsuit in the United States over its hit song "Swim," released in March.

According to Billboard, songwriters Steve Cooper, Jon Sandler, and Greylyn Johnson filed the lawsuit in California on July 8, alleging that "Swim" copied substantial elements of an unreleased song bearing the same title.

"Upon listening several times [to 'Swim'], plaintiffs came to what they considered to be the obvious and inescapable conclusion that [it] copied in very large part the original work and clearly infringed their copyrights," the complaint stated.

Named as defendants are HYBE, HYBE America, BigHit Music, and several of the song's credited writers, including Ryan Tedder.

The plaintiffs said they began circulating copies of their demo in March last year to various parties, including Artist Publishing Group, before BTS released "Swim."

After the song's release, the plaintiffs' legal team retained musicologist Alexander Stewart to compare the two works.

In his report, Stewart alleged that "Swim" borrowed several key musical elements from the demo, including its signature title hook, distinctive harmonies, textures, rhythmic patterns, and lyrical components.

"These similarities encompass the signature phrase (or 'hook') referencing the title, unusual harmonies, textures, and rhythmic and lyrical elements. In my expert opinion, independent creation by BTS can be ruled out and copying is the inescapable conclusion," Stewart wrote.

Neither HYBE nor BigHit Music had publicly responded to the lawsuit as of posting.

The case marks the latest legal challenge involving a major K-pop act and comes as BTS continues its long-awaited return to full-group activities following the completion of the members' mandatory military service.

BTS in London (X)