A controversial proposal allowing the government to pull the plug on Web sites accused of aiding piracy is closer to becoming a federal law.

After a flurry of last-minute lobbying from representatives of content providers including the Motion Picture Association of America (MPAA) and the Recording Industry Association of America (RIAA), a Senate committee approved the measure today by a unanimous vote.

In the last week, support for the bill known as COICA, for Combating Online Infringement and Counterfeits Act, broadened beyond groups traditionally active in online copyright disputes to include the Newspaper Association of America, which said the legislation was needed because online piracy "undermines the investments that newspapers make in journalism." Labor unions, including the International Brotherhood of Teamsters, argued that American workers "have suffered significant harm due to theft of copyrighted and trademarked goods."

An ad appeared in a newspaper targeting Capitol Hill yesterday signed by groups including Major League Baseball, the NFL, Nintendo, and Viacom. The U.S. Chamber of Commerce pressed Congress to move quickly, and even Rob McKenna, Washington state attorney general, signed on to the effort.

"Those seeking to thwart this bipartisan bill are protecting online thieves and those who gain pleasure and profit from de-valuing American property," Mitch Bainwol, RIAA chairman, said after today's vote. "We congratulate Chairman Leahy and Senator Hatch for their leadership on this bill and to the Senate Judiciary Committee for its action today." (Patrick Leahy, a Vermont Democrat and chairman of the Senate Judiciary committee, and Orrin Hatch, a Utah Republican, are cosponsors of COICA.)

The sentiment is not universal: Since its introduction in September, COICA has alarmed engineers and civil liberties groups, who say that it could balkanize the Internet, jeopardize free speech rights, and endanger even some legitimate Web sites. Its wording says that any domain name "dedicated to infringing activities" could find itself in the U.S. Department of Justice's prosecutorial crosshairs.

Peter Eckersley, a technologist at the Electronic Frontier Foundation, wrote earlier this week that the bill will create a 1950-style Hollywood blacklist with the government deciding which Web sites are legitimate or not. The federal government will be forced "into the swamp of trying to decide which websites should be blacklisted and which ones shouldn't," Eckersley said. "And they're going to discover that the line between copyright infringement and free political speech can be awfully murky."

At the same time, a group of law professors wrote an open letter (PDF) to the Senate saying the law is unconstitutional under the First Amendment and "would set a dangerous precedent with potentially serious consequences for free expression and global Internet freedom."

Someone who knows the Internet Protocol address--the IP address for cnet.com, for instance, is currently 216.239.113.101--would still be able to connect to the Web site even if the computer that normally translates a domain name into its numeric address pretends not to know it.

If all copyright- and trademark-infringing Web sites were hosted in the United States with their Webmasters living on U.S. soil, Leahy's COICA would be mostly unnecessary. A straightforward copyright lawsuit of the sort that the RIAA and the software industry have spent years perfecting would suffice.

But that's not the case. Sites like the Russia-hosted MP3Sparks.com are accessible around the world, even though they almost certainly violate U.S. copyright law. ThePirateBay.org in Sweden has not only survived what seem like innumerable attempts to shut it down, but its operators take special pains to mock copyright lawyers who write cease-and-desist letters meant to be both earnest and threatening.

A Web site is in danger of having its domain seized (or having U.S. Internet providers encounter a sudden case of amnesia when their customers try to visit it) if it is "primarily designed" and "has no demonstrable, commercially significant purpose or use other than" offering or providing access to unauthorized copies of copyrighted works. Counterfeit trademarks--that's why Chanel, Nike, Tiffany, and LVMH Moet Hennessy Louis Vuitton also signed the letter--are also included.

The wording is significant. Because the phrase "providing access" appears, that would include specialty search engines including The Pirate Bay that provide links to copyrighted works, even if the actual files are available through BitTorrent elsewhere.

If COICA becomes law, domain name registries such as Verisign, which owns the rights to .com, .net, .tv, .cc, and others would find themselves under new and uncomfortable legal pressure. The .org registry has been run by the Public Interest Registry since 2003. (The law professors' letter says: "For the first time, the United States would be requiring Internet Service Providers to block speech because of its content.")

But registries for top-level domains in other countries would remain unaffected, and The Pirate Bay, perhaps as a precautionary measure, already owns thepiratebay.se. Americans interested in free (if illegal) downloads could switch to an offshore domain name service or visit The Pirate Bay's IP address at http://194.71.107.15, which means that this congressional effort might accomplish less than its backers would like.

One open question: whether the lame duck Congress currently in session has time to enact COICA, which would mean votes in the House of Representatives as well. Even with this breadth of support, the odds are against it.

Update 11:30 a.m. PT: I received an e-mail from Gigi Sohn of Public Knowledge, which the RIAA said was "protecting online thieves" by opposing the bill. Sohn said: "And they are willing to throw free speech, International cooperation, due process, and the proper functioning of the Internet in the trash in the hope of shutting down a few bad actors. Their goal could be accomplished in a way that doesn't have those consequences, but the media conglomerates aren't interested."