The man who wrote "Grandma Got Run Over by a Reindeer" wants his piece of the digital pie, and he's found some allies in the Allman Brothers Band and Cheap Trick.

Elmo Shropshire, a Marin County, California, veterinarian who tours as Dr. Elmo, joined the Allmans and Cheap Trick in their lawsuit against Sony Music, filed in April, over royalties paid to artists for digital download sales. The artists contend that the label uses an unfair formula to calculate the percentage of digital sales that go to artists.

Dr. Elmo joined the lawsuit earlier this month when it was refiled to add ringtone sales to the claim that the label giant wasn't paying artists enough from songs sold on digital services like iTunes and Napster.

Elmo told MP3.com that his song's holiday appeal has made it a big download hit in recent years.

"It was a really big download around Christmas time last year, that's for sure," he said. The money he's lost from Sony's formula compared to what he think he should be paid "is almost enough for me to have paid for an attorney to file this case on my own."

The class-action lawsuit claims that the artists' contracts require Sony to pay its artists about 30 cents out of every 70 cents it gets for digital downloads--out of a total of 99 cents that digital shops like iTunes charges per song. But the complaint maintains that Sony is only paying artists 4.5 cents for each song.

For individual ringtones, artists have been paid slightly more than 8 cents, according to the lawsuit, out of the $1 to $1.50 that Sony Music gets from each sale. The musicians say they should get 50 to 75 cents.

The suit centers on whether artists should be paid for digital sales like the way they would be for a CD, whereby a label can deduct costs for packaging, breakage, and returns, or as a licensed song, as an artist would do for a car commercial, for instance.

Sony Music could not be reached for comment.

"Seems to me like it's a very cut and dry case, but somehow they never turn out that way once it goes to court," Elmo said.