The US Supreme Court is weighing in on the first RIAA file sharing case to reach its docket, requesting that the music labels’ litigation arm respond to a case testing the so-called “innocent infringer” defense to copyright infringement.

The case pending before the justices concerns a federal appeals court’s February decision ordering a university student to pay the Recording Industry Association of America $27,750—or $750 a track—for file-sharing 37 songs when she was a high school cheerleader. The appeals court decision reversed a Texas federal judge who, after concluding the youngster was an innocent infringer, ordered defendant Whitney Harper to pay $7,400—or $200 per song. That’s an amount well below the standard $750 fine required under the Copyright act.

Harper is among the estimated 20,000 individuals the RIAA has sued for file-sharing music. The RIAA has decried Harper as “vexatious,” because of her relentless legal jockeying.

The justices, without comment, asked the RIAA to respond (PDF) to Harper’s petition to review the appellate court’s ruling. (The RIAA had originally waived its right to respond to the petition.)

Harper’s challenge weighs whether the innocent infringer defense to the Copyright Act’s minimum $750-per-music-track fine may apply to online file sharing. Generally, an innocent infringer is someone who does not know she or he is committing copyright infringement.

The justices have not granted review of Harper’s case, but Wednesday’s action by the high court substantially increases the chances that an RIAA file-sharing case targeting an individual will be heard for the first time, sometime in the upcoming term that begins October 4.

The high court usually grants less than one percent of petitions sent to it. According to a recent study, if the court requests briefing on a petition, as it did on the Harper case, the odds increase to 34 percent.

A Texas federal judge had granted Harper the innocent-infringer exemption to the Copyright Act’s minimum fine, because the teen claimed she did not know she was violating copyrights. She said she thought file-sharing was akin to internet radio streaming.

The appeals court, however, said she was not eligible for such a defense, even though she was between 14 and 16 years old when the infringing activity occurred on LimeWire. The reason, the appeals court concluded, is that the Copyright Act precludes such a defense if the legitimate CDs of the music in question carry copyright notices.

“Harper cannot rely on her purported legal naivety,” the New Orleans-based 5th U.S Circuit Court of Appeals ruled, 3-0.

Attorneys for Harper told the justices (PDF) that she should get the benefit of the $200 innocent-infringer fine, because the digital files in question contained no copyright notice.