As Internet giants go dark Wednesday to protest SOPA, the bill that aims to allow intellectual property owners to go after alleged content pirates, the U.S. Supreme Court Wednesday issued a ruling giving Congress broad authority to grant copyright protection and control the size of the public domain.

The court held in a 6-2 decision that the public domain -- the pool of content any one can perform, share or reproduce without getting approval from the creators of that content -- can shrink and grow at Congress' whim. This ruling rejected the arguments of orchestra conductors and musicians who challenged lawmakers' authority to give millions of foreign works created after 1923 retroactive U.S. copyright protection in 1994. Before this, for example, Walt Disney dipped into the public domain to produce an animated version of Peter and the Wolf without paying its composer, Sergei Prokofiev. On a smaller scale, orchestras freely performed works from the classic repertoire.

Justice Ginsburg's Majority Opinion

Justice Ruth Bader Ginsburg, writing for the majority, rejected the notion that artistic works are locked into the public domain.

Neither the Copyright and Patent Clause nor the First Amendment, we hold, makes the public domain, in any and all cases, a territory that works may never exit, Ginsburg said in the opinion for the 6-2 ruling.

Conductor Lawrence Golan, the lead plaintiff in the suit, challenged the U.S.'s ability to grant copyright protection to work already in the public domain, arguing that it violated the Constitution's Copyright and Patent Clause and the First Amendment.

Much of Golan's argument rested on the idea that the Constitution places a limited time on copyright protection to promote the progress of knowledge that will benefit the public. In the case of these foreign works, Golan argued that the limit the U.S. placed on their protection was zero, in that Congress provided no copyright protection at all.

Ginsburg rejected the argument, recounting laws passed in the 18th and 19th centuries that protected already-published maps and books; inventions and works that slipped through the cracks; photographs; and dramatic works.

If Congress could grant protection to these works without hazarding height­ened First Amendment scrutiny, she wrote, then what free speech principle disarms it from protecting works prematurely cast into the public domain.

Works such as Fritz Lang's Metropolis, Stravinsky symphonies, Picasso pieces and J.R.R. Tolkien's Lord of the Rings trilogy had received copyright protection in the United States following a multinational trade deal the U.S. Congress ratified in 1994, called the Uruguay Roundtable Agreement.

These works were not compensated for the amount of time they went unprotected in the U.S.; they will enter the public domain as scheduled, as if they had U.S. copyright protection all along.

In dissent, Justice Stephen Breyer said Congress' decision on foreign works flies in the face of the Copyright Clause's incentive for the creation of new works. He also feared that a smaller public domain will spur piracy, noting the difficulty and costly process of tracking down foreign copyright owners for obscure or old works.

These high administrative costs can prove counterproductive in another way, Breyer said. They will tempt some potential users to 'steal' or 'pirate' works rather than do without. And piracy often begets piracy, breeding the destructive habit of taking copyrighted works without paying for them, even where payment is possible.