Eminem Eminem

Eminem is going up against the mother of all music companies — Universal Music Group — over digital royalties in the first legal test for the issue that is a major concern for artists.

The rapper's two-year-old lawsuit in U.S. District Court for the Central District of California went to trial Tuesday and could affect a bevy of musical artists and digital downloads over iTunes, according to The Wrap.

The rapper's publishing company, F.B.T. Productions, is suing over how much he is entitled to when UMG sells his music to third-party distributors, such as iTunes and phone companies, which offer the music for ringtones.

The defendants argue that the plaintiffs have misconstrued the contracts with UMG.

What's at stake? Only hundreds of millions of dollars for recording artists with massive distribution through digital downloads.

The witness list for the case consists of several heavy hitters, including Jimmy Iovine, founder of UMG and Steve Jobs, CEO of Apple.

Eminem is not expected to be present.