A federal law aimed at curbing Internet pornography violates Americans' free speech rights and is unconstitutional, an appeals court ruled Thursday.

For the second time, the 3rd U.S. Circuit Court of Appeals in Philadelphia struck down a law that would imprison commercial Web site operators who do not cordon off sexually explicit material from minors. The Child Online Protection Act (COPA) "is not narrowly tailored to proscribe commercial pornographers and their ilk, as the government contends, but instead prohibits a wide range of protected expression," the court said.

"The analysis is the one we were making from the very beginning, which is that the law makes it a crime to communicate speech that is clearly protected (by the First Amendment) to adults," said Ann Beeson, an attorney at the American Civil Liberties Union who litigated the case. "The only way someone can avoid prosecution is to set up burdensome screening systems. The impact is so great it violates the First Amendment."

This decision is unusual because it's the second time the 3rd Circuit has rejected COPA as violating the First Amendment's guarantee of freedom of expression. In May 2002, the U.S. Supreme Court reviewed the case, but said the 3rd Circuit's earlier decision was insufficient to establish that COPA was unconstitutional.

In its opinion, released Thursday, the 3rd Circuit adopted a far more exhaustive approach, ruling that COPA was not narrowly tailored to target only pornography and that legitimate Webmasters would be unfairly targeted. COPA makes it a crime to publish "any communication for commercial purposes that includes sexual material that is harmful to minors, without restricting access to such material by minors." The maximum penalty is a $50,000 fine, six months in prison and additional civil fines.

"COPA will likely deter many adults from accessing restricted content, because many Web users are simply unwilling to provide identification information in order to gain access to content, especially where the information they wish to access is sensitive or controversial," the court said. "People may fear to transmit their personal information, and may also fear that their personal, identifying information will be collected and stored in the records of various Web sites or providers of adult identification numbers."

The U.S. Justice Department, which is defending the law, could appeal its loss to the Supreme Court a second time. A representative could not be reached for comment Thursday.

In the previous round, in 1999, the 3rd Circuit relied primarily on COPA's definition of "community standards," concluding that Web sites that would be perfectly legal in liberal areas of the United States could be viewed as unlawful in more conservative jurisdictions.

The Supreme Court rejected that as an insufficient argument against the law. A plurality opinion written by Justice Clarence Thomas said, "If a publisher chooses to send its material into a particular community, this court's jurisprudence teaches that it is the publisher's responsibility to abide by that community's standards. The publisher's burden does not change simply because it decides to distribute its material to every community in the nation."

In fact, said Thomas, "If a publisher wishes for its material to be judged only by the standards of particular communities, then it need only take the simple step of utilizing a medium that enables it to target the release of its material into those communities."

Only Justice John Paul Stevens thought that the problems with variable "community standards" were by themselves sufficient to eviscerate COPA. "In the context of the Internet...community standards become a sword, rather than a shield," Stevens wrote in his lone dissent. "If a prurient appeal is offensive in a puritan village, it may be a crime to post it on the World Wide Web."

Plaintiffs in the COPA case include the American Booksellers Foundation for Free Expression, Salon.com, ObGyn.net, Philadelphia Gay News and the Internet Content Coalition. CNET Networks, publisher of News.com, is a member of the Internet Content Coalition.

COPA represents Congress' second attempt to restrict sexually explicit material on the Internet. The Supreme Court in 1997 rejected the Communications Decency Act, which covered "indecent" or "patently offensive" material, as unconstitutional. On Wednesday, the court heard oral arguments on a separate law that requires libraries accepting federal funds to install controversial filtering software.