Eminem has taken his record label Universal Records to court for allegedly underpaying him on royalties from digital downloads.
Marshall Mathers publishing company FBT Productions says the label owes him over 800,000.
Shady's lawyers argue that money from iTunes and other download services should fall under licensing agreements in his contract not distribution.
The court case will be very important for the whole music industry as the judgement will set a precedent for other artists.
Apple boss Steve Jobs and Universal boss and Eminem mentor Jimmy Iovine are both expected to testify.
The courtcase is unlikely to effect the release of Slims new album Relapse- which should be out this Spring but has yet to be given a release date.