The music publisher representing rapper Eminem has filed suit against Apple Inc. for what it claims is the unauthorised sale of the artist's music on the iTunes store.

According to the Detroit News, publisher and copyright manager Eight Mile Style and Martin Affiliated filed the suit in a US District Court in Eminem's hometown of Detroit, Michigan.

The firm claims that through a deal with Eminem's record label, Universal, Apple has been selling the artist's songs without the publisher's permission. Eight Mile Style and Martin Affiliated reportedly asked Apple to halt the downloads, but the company refused.

The company reportedly acknowledged that it was receiving royalties from the downloads, but contends that the distribution is still being done over the objections of the artist and his publisher.

This is not the first time that the controversial rapper has been in the limelight for his stances on copyright protection and digital rights management (DRM) software for music distributed over the internet.

In 2002, Eminem was one of the first artists to adopt the use of CD copy-protection programs.

The news also comes at a time when relations between Apple and Universal are said to be on the rocks.

Early this month it was reported that Universal was balking at renewing its deal with Apple, primarily due to chief executive Steve Jobs' stance on DRM and the company's refusal to raise song prices.