Attorneys representing the rapper’s publishing companies, Eight Mile Style and Martin Affiliated, filed a lawsuit in U.S. District Court in Detroit in an attempt to stop five companies from selling Eminem ring tones on the Internet, according to The Associated Press. Cellus USA, FanMobile, Nextones.com, MyPhoneFiles and MatrixM are named in the suit. The lawyers also plan to sue karaoke companies that sell Eminem songs for sing-along CDs without first obtaining the proper licenses.

“This is a big business,” said attorney Howard Hertz, a representative for the plaintiffs. “We’re talking hundreds of thousands of dollars a year.”

Ring-tone revenue has recently exploded, according to a Jupiter Research report published earlier this year, more than doubling to $217 million in 2004 with expectations that it will more than triple by 2009.

Eminem has not been seen since early August, when he abruptly canceled a European tour citing “exhaustion.” Two days after the cancellation, his spokesperson confirmed that Em had checked into a drug-rehabilitation facility to treat a dependency on sleep medication. Late last week, the spokesperson said there was no update on Em’s condition or whether he’d been released from the facility.