(CNN) -- That was a pretty catchy, sing-songy version of Sir Mix-A-Lot's rap hit "Baby Got Back" in Thursday night's episode of "Glee." It was also very familiar to fans of indie singer-songwriter Jonathan Coulton.
As angry Coulton fans are clamoring on Twitter, Coulton arranged and recorded an eerily similar "Baby Got Back" cover. So similar, in fact, that the "Glee" version included Coulton's line "Johnny C's in trouble," replacing the lyric "Mix-A-Lot's in trouble" in the original song.
Coulton said he was not informed beforehand, nor was he given any credit or compensation for having arranged the melody of the cover song. What's more, he says, Fox Broadcasting representatives told Coulton's representatives that "they're within their legal rights to do this, and that I should be happy for the exposure," he wrote on his blog, "even though they do not credit me, and have not even publicly acknowledged that it's my version -- so you know, it's kind of SECRET exposure."
A representative from 20th Century Fox Television told CNN Friday the network is not commenting on the matter.
Coulton, known for nerdy and humorous songs such as "Code Monkey," said Friday that he is "mystified" about why the show went about using the cover song in this way.
"Glee has a reputation for being a show that celebrates the underdog," he said, before catching a plane to San Francisco. "It's the anti-bullying show. But this is a bullying way to approach this."
When it comes to copyright protection, however, there's a distinction between what might seem ethical and what is legal, lawyers say.
The rights to "Baby Got Back" belong with songwriter Anthony L. Ray, also known as Sir Mix-A-Lot, and his music publisher, Universal, who have apparently given proper licenses to Fox and "Glee," said Kevin Parks, a copyright attorney with the Leydig law firm in Chicago who does not represent any party involved in what Twitter users are calling #JoCoGleeGate.
Because Coulton's cover is derivative of the original work by Sir Mix-A-Lot, Coulton does not have a copyright claim against "Glee" for using the Coulton version, Parks said.
Covers don't get their own copyright protection as far as the underlying musical composition, Parks said. But Coulton might have legal footing if the show used Coulton's audio track.
"If 'Glee' used parts of Coulton's actual recording, there would be a copyright claim for him to pursue," Parks said. "If not, Coulton's gripe may have moral weight, but not the force of law."
Fans of Coulton are not taking this lightly. Some are undertaking sophisticated audio analyses of both song versions, Coulton said. One called "alacrion" created a side-by-side comparison of the two songs on SoundCloud, demonstrating a remarkable resemblance. A fan named Paul Potts posted his own investigation into the similarities of the audio, which he called "pretty convincing."
"Hilariously, for me, it comes down to the sound of a duck quacking, which is a sound effect that was in my version, used as a bleep noise to cover up an expletive," Coulton said. "While it is very hard to hear, if I at home mess with the equalizer settings and some filters, I can actually hear that quack is in that mix."
From this, Coulton believes at least some of his audio was used by the show, although he is unsure how much. Potts explored this quack issue as well, but wrote on his blog that he identified the "ghost of the quack."
There have been infringement cases involving rap songs that sampled even four to eight seconds of other songs, and that was deemed illegal, said Mark Lemley, director of the Stanford University program in law, science & technology who is also not representing anyone in this controversy.
It may seem like an artist should get paid if his song, whether a cover or something else, is imitated elsewhere, but this is "one of those holes in the law that just doesn't end up giving the owner of the sound recording copyright much in the way of rights," Lemley said.
Coulton said his lawyer is in touch with "the people at 'Glee.'"
Geek celebrities such as the band They Might Be Giants and podcaster Chris Hardwick came out in support of Coulton on Twitter.
Astronomer Phil Plait, author of Slate's "Bad Astronomy" column, tweeted with a link to another story about the debacle: "I'll admit it: I used to watch and enjoy Glee. Not any more. It's dead to me."
As of this writing, Sir Mix-a-Lot has not responded on his own Twitter account.