Last year, the lower court decided that software was an equally effective, and less restrictive, way to prevent children from viewing sexually explicit material online.
The federal government appealed that decision to the Supreme Court, arguing that half of American homes where children can access the Internet lack filtering software or other technology to block obscenity.
The American Civil Liberties Union challenged the law and argued that filters are more effective than a U.S. ban, which cannot be applied to foreign Web sites. The law also failed to cover e-mail, newsgroups, and chat rooms, which are used to disseminate pornography.
This week, the Supreme Court dismissed the appeal, in Mukasey v. ACLU, without comment. That prevents the Act from taking effect.
COPA was Congress' second attempt to restrict sexually explicit and indecent material on the Internet. In 1996, the Supreme Court rejected a similar law that was broader in scope.