The Supreme Court upheld a law Wednesday that extended U.S. copyright protection to books, musical compositions and other works by foreign artists that had been available without paying royalties.

The justices said in a 6-2 decision Wednesday that Congress acted within its power to give protection to works that had been in the public domain. The law's challengers complained that community orchestras, academics and others who rely on works that are available for free have effectively been priced out of performing "Peter and the Wolf" and other pieces that had been mainstays of their repertoires.

The case concerned a 1994 law that was intended to bring the U.S. into compliance with an international treaty on intellectual property. The law made copyright protection available to foreign works that previously could not have been copyrighted.

The court ruled in 2003 that Congress may extend the life of a copyright. Wednesday's decision was the first time it said that published works lacking a copyright could later be protected.

"Neither congressional practice nor our decisions treat the public domain, in any and all cases, as untouchable by copyright legislation. The First Amendment likewise provides no exceptional solicitude for works in the public domain," Justice Ruth Bader Ginsburg said in her opinion for the court.

But Justice Stephen Breyer, writing for himself and Justice Samuel Alito, said that an important purpose of a copyright is to encourage an author or artist to produce new work. "The statute before us, however, does not encourage anyone to produce a single new work. By definition, it bestows monetary rewards only on owners of old works," Breyer said.