Metallica attorney Howard King said Tuesday the move is a response to Napster's request for the information. Metallica has filed suit against Napster, alleging that the company infringed its copyrights.
Metallica's Lars Ulrich reportedly plans to deliver the 335,435 names to Napster's San Mateo, Calif., offices Wednesday.
The names were gathered by NetPD, a consulting firm hired by Metallica to monitor the site between April 28 and April 30.
Napster's service allows users to trade digital music files with one another. According to a statement from the band, users on average offer five songs for trading.
Napster could not immediately be reached for comment.
In response to the lawsuit, "(Napster) said tell us who's violating the copyrights and we'll remove them," King said. "If they are going to do what they say, their policy is they'll follow through."
King said the names were not being added to the lawsuit against Napster, but he did not rule out naming the users as defendants.
King, who also represents rap artist Dr. Dre in a similar suit against Napster, said that if the users are kicked off the service more artists may seek similar remedies. Napster has also been sued by the Recording Industry Association of America.
"If Napster honors their policy and obligations, we will make a submission on behalf of Dr. Dre," he said. "I think you'll see musicians around the world make submissions. You'll see a flood of requests from musicians."
Last week, online music firm MP3.com Inc. (mppp) lost a copyright violation suit brought by record labels. The company could face fines of more than $750 million in the case. The MP3 suit involved the company's creation of a database of songs for its MyMP3 service. The suit argued that the database itself constituted copyright violation, even though consumers would theoretically not be able to access songs in the database unless they already owned copies of the songs.
King said the MP3.com ruling was "heartening."
"The legal issues are different," he said. "MP3.com, in my opinion, was operating a lot closer to the legal lines than Napster is. What Napster is doing is far more illegal than MP3 so (the federal court ruling) is heartening."
Metallica will discuss the Napster suit with fans at an online chat hosted by Artistsdirect.com at artistdirect.com/metallica at 5 p.m. PT Tuesday evening.