The US Supreme Court on Wednesday upheld a law extending copyright protection to foreign works -- everything from Prokofiev's "Peter and the Wolf" to Picasso's "Guernica" -- even after they have entered the public domain.

The court ruled 6-2 that a 1994 law that brought the United States in line with global intellectual property conventions violated neither US copyright law nor free-speech rights guaranteed by the constitution.

Congress therefore has the authority to pull works that are in the public domain and put them back under copyright protection.

The case centered on US efforts to get in line with the 1886 Berne Convention protecting literary and artistic works. The United States did not join the Convention until 1989.

In 1994, to improve US implementation of Convention rules, and as part of the US response to the Uruguay Round of World Trade Organization talks, Congress granted foreign works under copyright protection the same protection available to US works.

The chief plaintiff in the case was Lawrence Golan, a University of Denver orchestra conductor, who said his students cannot play "Peter and the Wolf" without paying royalties.

The plaintiffs, which included musicians, professors and film distributors, claimed that the law was an infringement on their right to free speech. Their argument was supported by Internet titan Google as well as the American Civil Liberties Union.

In the court ruling Justice Ruth Bader Ginsburg wrote that the 1994 law required that the right to perform "Peter and the Wolf" must now "be obtained in the marketplace."

She added that this was the same marketplace for US composers with copyright protection like Aaron Copeland and Leonard Bernstein, and US performers have managed to pay royalties for performing these works.

The 1994 law gives foreign copyright holders the assurance that their works will be protected under US copyright law "for the remainder of the term of their protection in their home country," Ginsburg wrote.

Justice Elena Kagan did not take part in the ruling, while Justices Stephen Breyer and Samuel Alito dissented.