Now

Napster

has another lawsuit to deal with.

A judge said yesterday that the song-swapping online service has to block copyrighted songs from being traded on its system, and today online downloadable music retailer

EMusic.com

(EMUS)

filed suit against Napster. EMusic claims what others have all along -- that Napster infringes on the copyrights of songs to which Emusic has the rights.

The suit was filed in the same U.S. District Court in San Francisco that issued the injunction against Napster. EMusic, which sells music in the form of MP3 files to users for a fee, said yesterday's injunction is a "major step towards leveling the playing field" for downloadable music companies.

TheStreet Recommends

An EMusic spokesman said the company hasn't determined the number of songs that have been allegedly traded illegally on Napster. However, he did say that "we are asking for the full, high end of damages which is $150,000 per infringement."

Representatives for Napster weren't immediately available for comment.

On Tuesday, U.S. District Court Judge Marilyn Hall Patel issued a

new injunction that requires Napster to prevent copyrighted music files from being swapped on its system within three days of notification from the copyright holders.

EMusic said it owns the rights to about 160,000 tracks, including songs from bands and artists such as Elvis Costello, Phish, Green Day and Kenny Rogers.

Shares of EMusic fell 3 cents, or 8.3%, to 31 cents in recent

Nasdaq

trading.