A bill introduced in the California Legislature last Friday seeks to do what U.S. federal courts have so far refused to do: criminalize selling, advertising, and distributing peer-to-peer (P2P) file-sharing software

Written by state Senator Kevin Murray (D), a longtime lawmaker from Los Angeles with close ties to the entertainment industry, the legislation is aimed straight at the business plans of file-sharing companies such as Grokster, Morpheus, and Kazaa. The bill would make it a crime to sell file-sharing software without taking ?reasonable care? to prevent copyright infringement and pornography swapping.

On Tuesday, file-sharing proponents blasted the bill. ?It?s another edge of a sword that the entertainment cartel is attempting to use to gut the P2P application,? said Matthew A. Neco, general counsel and vice president for StreamCast Networks. Based in Woodland Hills, California, StreamCast Networks makes Morpheus, a file-sharing program boasting 124 million downloads worldwide.

File-sharing companies are at loggerheads with the entertainment industry, which claims the technology allows users to break the law every time they download a song or other copyrighted material for free. Other file-sharing foes charge it permits the easy flow of pornography between minors. In August, a federal court in California ruled that file-sharing companies are not violating copyright law when customers use their programs to trade copyrighted music, text, or video. The U.S. Supreme Court will hear the case in March.

The stakes are getting higher due to new software that speeds the transmission of video over file-sharing networks. Hollywood fears the new technology, known as BitTorrent, which could make downloading a movie as simple and fast as downloading a song.

Mr. Murray said he wrote the bill because file-sharing companies have the ability, as well as the legal responsibility, to monitor the ways their programs are used. ?Even if you aren?t selling crack, you can?t have a crack house,? said Mr. Murray. He said the law would not require major investments from file-sharing companies: ?We are asking for filters, not perfect filters.?

Adam Eisgrau, the executive director of P2P United, the file-sharing industry?s trade association in Washington, D.C., said he is not aware of similar efforts in other state capitols to squelch file-sharing. But California?s position as the richest, most populous state in the U.S. makes legislation from the state capital in Sacramento worth watching. ?As California goes, so may the nation go,? said Mr. Eisgrau.

Both Mr. Eisgrau and Mr. Neco said the California bill might be unconstitutional because it violates First Amendment protections of free speech, and hinders interstate commerce.

Mr. Murray, a 10-year veteran of California politics, has often been a critic of the music industry, claiming that recording contracts turned musicians into indentured servants. His new bill puts him on the same side of a hot-button issue with his former opponents.

Campaign finance records show that Mr. Murray received $5,000 from Don Henley in 2003. The former front man for the Eagles, the 1970s rock band famous for the hit ?Hotel California,? has been an outspoken opponent of the recording industry and file-sharing software. Both houses of the California Legislature must pass the bill, and Governator Arnold Schwarzenegger must sign it, before it becomes law.