U.S. District Judge Marilyn Hall Patel said that 70 million people are expected to be using Napster by year’s end and “what lures them is the infringing use.”

Patel said the temporary injunction will go into effect at midnight PDT July 28.

The Recording Industry Association of America sued Napster in December for copyright infringement and related state law violations. The association accused Napster of encouraging users of the company’s software and computer servers to trade copyrighted music online without permission.

Napster had initially responded to the suit by telling the court it was entitled to federal protections as an Internet service provider, but on May 9, Patel rejected the claim that the Digital Millennium Copyright Act of 1998 protected the company from the illegal actions of its users.

Napster later adjusted its defense strategy, arguing that personal copying of music is protected by federal law.

The dispute over the free trade of information and the concerns of copyright holders have come to a head in the ongoing battle over Napster. Heavy metal band Metallica has been particularly outspoken against Napster and sued the company for copyright infringement after the band found more than 300,000 users trading its songs online.

In response, Napster blocked access to its service for more than 30,000 of those users identified by Metallica, but new users log on daily and continue trading the band’s music.

It remains unclear whether Internet music file-swapping is so bad for the music industry after all.

A recent study of more than 2,200 online music fans by Jupiter Communications suggests that users of Napster and other music-sharing programs are 45 percent more likely to increase their music purchasing than fans who aren’t trading digital bootlegs online.

“Clearly, people who are using Napster love music. They’re probably our best customers,” said Hilary Rosen, president of the RIAA.

The RIAA estimates that song-swapping via Napster by an estimated 20 million people worldwide has cost the music industry more than $300 million in lost sales.

“All of this litigation is really setting the groundwork for what is going to be the future of the Internet,” said Larry Iser, an intellectual property attorney.