COPA, which was sponsored by Rep. Michael Oxley (R-Ohio), is an attempt to construct a version of the Communications Decency Act that would stand up to constitutional muster. A federal judge in Philadelphia blocked the law's implementation in late 1998, however, agreeing with an ACLU claim that it amounted to censorship.

The ACLU and other groups argued that the law could prevent children from looking at non-pornographic Web sites that contained material about sex, such as sex education material posted on sites sponsored by groups like Planned Parenthood.

In a dissenting opinion to today's ruling, Justice Stephen Breyer wrote, "In sum, the Act at most imposes a modest additional burden on adult access to legally obscene material, perhaps imposing a similar burden on access to some protected borderline obscene material as well."

One COPA supporter said that the court is exceeding its powers. "This is akin to judicial tyranny," said Patrick Trueman, senior legal adviser at the Family Research Council and former chief of the child exploitation unit at the Justice Department's Criminal Division. "The court is dismissing acts of Congress which reflect the will of the people... This decision says to pornographers that you have a green light to distribute material to children."

The U.S. Court of Appeals for the 3rd Circuit, located in Philadelphia, originally ruled COPA unconstitutional in 2000. The Supreme Court later upheld a portion of the law dealing with the use of community standards to determine what material is harmful to minors. But the court sent the case back to the appeals court, refusing at that time to rule on the free-speech issues. The appeals court again found the law unconstitutional and the Justice Department once again appealed that decision. The most recent arguments before the Supreme Court were held in March of this year.

John Morris, staff counsel for the Center for Democracy and Technology, a Washington-based technology policy think tank, said that technology has advanced since COPA became law, but "the ability of a Web site to insure that a minor is not surfing to [a pornographic] Web site has not fundamentally changed." He predicted that the case would spend several more years at the appeals level and eventually come back to the Supreme Court.

Morris said that instead of restricting access, parents should educate themselves about the Internet and teach children "how to comport themselves online."

While the Supreme Court has several times rejected attempts to limit what kind of material is available in cyberspace, it did uphold a law in June 2003 that withholds federal funds from schools and libraries unless they install software filters on their computers to block pornographic Web sites.

Today's majority ruling was authored by Justice Kennedy; his opinion was joined by Justices John Paul Stevens, David H. Souter, Clarence Thomas and Ruth Bader Ginsburg. The dissenting justices were Chief Justice William Rehnquist, Sandra Day O'Connor, Antonin Scalia and Stephen Breyer. The case is Ashcroft v. American Civil Liberties Union.