Congress should be careful as it considers the , said Representative Jared Polis, a Colorado Democrat. The bill, approved by the Senate Judiciary Committee in late May, would weaken the "underpinnings of the Internet," he said at an event announcing the study.

"These economic arguments are particularly important when there's a lot at stake -- jobs, jobs jobs," Polis said.

A spokeswoman for Senator Patrick Leahy, a Vermont Democrat and main sponsor of the PROTECT IP Act, did not immediately respond to a request for comment. The legislation would allow the U.S. Department of Justice to seek court orders requiring search engines and Internet service providers to stop sending traffic to websites accused of infringing copyright, and allow copyright holders to seek court orders requiring payment processors and online ad networks to stop doing business with the accused websites.

The Recording Industry Association of America defended the PROTECT IP Act. The bill "targets the worst of the worst illegal foreign sites that profit from stealing American goods," Mitch Glazier, executive vice president of government and industry relations, said in a statement. "Any suggestion that these overwhelmingly illegal sites would fall under any kind of 'fair use' defense is wholly incorrect. The legislation attacks clearly illegal acts, and not the technology used to implement them."

Fair use exceptions allow people to use a portion of works protected by copyright without the owners' permission. Fair use limitations to copyright law allow people to excerpt a protected work for news reporting, criticism, teaching and research. Fair use allows people to reverse engineer software, allows search engines to cache images and text, and allows TV viewers to tape programs and watch them later. It also allows consumers to sell or lend copies of music, books and other protected materials.