In court papers filed late Monday, the groups said that the Recording Industry Association of America (RIAA) has not followed the law in its efforts to learn more about a Kazaa user accused of illicitly trading music files.

Monday's move highlights the latest battle lines that have been struck in the legal war over peer-to-peer networks. On one side are Internet companies, civil liberties groups and telecommunications providers, an alliance that is opposed by the RIAA and the Motion Picture Association of America (MPAA).

The 30-page amicus brief, signed by 12 groups including the U.S. Internet Industry Association, the Computer and Communications Industry Association, and Yahoo, accuses the RIAA of hoping to turn Internet providers into copyright cops.

"What the RIAA is really seeking, at the end of the day, is to shift the burden of copyright enforcement from its own members--who apparently would prefer not to alienate potential customers by suing them outright--to an ISP that does nothing more than provide an Internet connection to the customer," the brief says.

"What we hope to accomplish is to force the RIAA to follow established legal procedures and due process," said David McClure, president of the U.S. Internet Industry Association, which organized the brief. "The music industry pays the RIAA to investigate and prosecute copyright infractions. They don't pay us a penny to do that. They don't pay ISPs a penny to do that. Even if they did, it would be a violation of due process and subscriber privacy."

Verizon's user allegedly has been swapping songs by artists including Billy Joel, Barry White, Aerosmith, Janet Jackson, Jennifer Lopez, N'Sync and Britney Spears.

At issue in the RIAA's request is an obscure part of the DMCA that permits a copyright owner to send a subpoena ordering a service provider to turn over information about a subscriber. It is not necessary to file a lawsuit to take advantage of the DMCA's expedited subpoena process.

Verizon and ISPs agree that the RIAA has the right to unmask a true copyright infringer. "A copyright holder can certainly, as Verizon suggested that the RIAA do in this case, file a 'John Doe' lawsuit and seek the identity of the customer through ordinary discovery methods," the amicus brief says.

Until now, the entertainment industry has relied on civil lawsuits aimed at corporations, not individuals, to limit widespread copyright infringement on peer-to-peer networks. Now, however, the RIAA is revising its strategy and appears ready to sue individuals swapping songs over the Internet.

The RIAA said its lawyers were reviewing the amicus brief and could not immediately comment.

In a statement, RIAA President Cary Sherman had accused Verizon of playing "a legal shell game" to save itself money.

"The only thing Verizon is protecting is Verizon's own business interests," Sherman said. "They are trying to avoid the cost of identifying infringers as provided for in the DMCA by imposing unrealistic and burdensome obligations on copyright owners instead."

RIAA said in a reply brief filed last week that Verizon had in the past turned over information about its DSL subscribers who were engaged in piracy--but had abruptly changed its mind. "Verizon’s newly minted legal position is baseless," the RIAA said.

It predicts a dire scenario will come to pass unless a federal judge, who has not ruled on the matter yet, allows the RIAA to use the DMCA subpoenas. "Like the sound recordings implicated by the RIAA's subpoena, the motion pictures produced and distributed by MPAA members are persistently subject to theft by Internet pirates. No tools are more critical in combating this digital piracy than the protections Congress enacted in the Digital Millennium Copyright Act," the MPAA said.

Megan Gray, an attorney who wrote an amicus brief in this case on behalf of civil liberties group, on Tuesday said: "The RIAA and other copyright holders are seeking to install a surveillance regime in which every ISP is acting as the bloodhound of a copyright holder. That, I am pleased to see, is being resisted by the ISPs and the civil liberties community."

The groups, including the Electronic Frontier Foundation, Consumer Alert, the Electronic Privacy Information Center, and National Consumers League, argued the RIAA is relying on a portion of the DMCA that violates Americans' right to be anonymous online. "Purported copyright owners should not have the right to violate protected, anonymous speech with what amounts to a single snap of the fingers," the brief said.