The decision by the 3rd U.S. Circuit Court of Appeals in Philadelphia is the latest twist in a decade-long legal battle over the Child Online Protection Act. The fight has already reached the Supreme Court and could be headed back there.

The law, which has not taken effect, would bar Web sites from making harmful content available to minors over the Internet. The act was passed the year after the Supreme Court ruled that another law intended to protect children from explicit material online — the Communications Decency Act — was unconstitutional in the landmark case Reno v. American Civil Liberties Union.

The ACLU challenged the 1998 law on behalf of a coalition of writers, artists, health educators and the publisher Salon Media Group.

ACLU attorney Chris Hansen argued that Congress has been trying to restrict speech on the Internet far more than it can restrict speech in books and magazines. But, he said, "the rules should be the same."

Indeed, the Child Online Protection Act would effectively force all Web sites to provide only family-friendly content because it is not feasible to lock children out of sites that are lawful for adults, said John Morris, general counsel for the Center for Democracy & Technology, a civil liberties group that filed briefs against the law.