Osbourne is seeking unspecified damages in the dispute
Black Sabbath singer Ozzy Osbourne is suing the band's guitarist Tony Iommi over royalty payments.
The 60-year-old has accused Iommi of falsely claiming to have sole rights to the band's name which has cost him royalties from merchandise sales.
Osbourne is seeking unspecified damages, lost profits and a declaration he is a half-owner of the trademark.
Iommi claims Osbourne legally relinquished rights to the band's name in the 1980s.
The guitarist registered the Black Sabbath trademark in the US in 2000.
Osbourne issued a statement on Friday asking Iommi to "do the right thing".
"Tony, I am so sorry it's had to get to this point by me having to take this action against you," he said.
"We've all worked too hard and long in our careers to allow you to sell merchandise that features all our faces, old Black Sabbath album covers and band logos, and then you tell us that you own the copyright."
Osbourne said he believed all four original members of the band should share Black Sabbath's name equally adding: "I hope that by me taking this first step that it will ultimately end up that way."
The star's lawyer has disputed he gave up rights to the band's name, saying that even if the singer did make such an agreement, he took a major role in the band's direction and success after rejoining it in 1997.
Black Sabbath, who were formed in Birmingham in 1968, have sold more than 100 million albums and are known for hits including Iron Man and Paranoid.