As you can probably guess, the legal action is about iTunes, with Eminem’s publisher, Eight Mile Style, and copyright manager, Martin Affiliated, claiming that iTunes is not authorized to sell the rapper’s songs.

“Eight Mile and Martin have demanded that Apple cease and desist its reproduction and distribution and Apple has refused,” reads the complaint.

But according to the Detroit News, Eminem’s publisher and copyright manager may have more than just Steve Jobs in their sights.

At stake is the question as to whether or not record labels have the right to green-light download sales for their artists. Current practices call for online music stores like iTunes and Napster to make agreements with record labels. However no such agreements are struck with publishers, mainly because labels are the traditional entities that negotiate sales rights.

And when it comes to downloads, there’s a big difference between sales agreements and licensing agreements.

Defining downloads as sales means that out of every 99 cent-per-track sale, iTunes gives a label about 70 cents, out of which about 9 cents goes to the publisher.

But treating downloads as licensing agreements would mean labels and publishers would split the 70 cents labels receive for each 99 cent download sale. So you can guess which definition music publishers prefer.

This isn’t the first legal fracas between forces representing the Real Slim Shady and Apple. Three years ago Eight Mile Style and Martin sued Apple over the unauthorized use of “Lose Yourself” in an iTunes / iPod commercial, and two years ago sued several companies for selling Eminem ringtones. Both suits were settled out of court.