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The justices without comment Wednesday rejected an appeal from the federal government to reinstate the Child Online Protection Act (COPA), passed by Congress in 1998.

WASHINGTON (CNN) - The Supreme Court has blocked further consideration of a federal law designed to keep sexual material from underage users of the Web.

The justices without comment Wednesday rejected an appeal from the federal government to reinstate the Child Online Protection Act (COPA), passed by Congress in 1998. The high court and subsequent federal courts said the law - which has never taken effect - had serious free speech problems.

The Bush administration was a strong supporter of the law and the Justice Department led the fight in court to revive it.

The justices issued their ruling a day after all nine were on hand for the inauguration of President Barack Obama. Retired Justice Sandra Day O'Connor also attended the ceremony.

The case tested the free speech rights of adults against the power of Congress to control Internet commerce. The Supreme Court twice previously ruled against COPA, leaning toward the argument that it represented government censorship rather than lawful regulation of adult-themed businesses. The law would have prevented private businesses from creating and distributing "harmful" content that minors could access on the Internet.

Free speech advocates said adults would be barred access to otherwise legal material, and that parental control devices and various filtering technology are less intrusive ways to protect children.

The high court in 2004 upheld a preliminary injunction against the law and sent the case back to lower courts for consideration of the arguments. In their opinion at the time, the 5-4 majority concluded COPA "likely violates the First Amendment."

"The government has not shown that the less restrictive alternatives proposed ... should be disregarded," Justice Anthony Kennedy wrote in the 2004 decision. "Those alternatives, indeed, may be more effective" than the law passed by Congress. "Filters are less restrictive" he said, and thus pose less risk of muzzling free speech. "They impose selective restrictions on speech at the receiving end, not universal restrictions at the source."

He added, "There is a potential for extraordinary harm and a serious chill upon protected speech" if the law takes effect."

In reconsidering the law, a federal appeals court in Philadelphia again ruled the law unconstitutional.

The case is Mukasey v. ACLU (08-565).