A federal judge in Charleston tossed out South Carolina's law barring distribution of sexually explicit pictures to minors over the Internet, ruling it violates the First Amendment and Congress' authority over interstate commerce.

U.S. District Judge Patrick Duffy, ruling Monday in a case brought by booksellers and publishers, noted Internet filters are an equally effective and less-restrictive alternative to keep such material from minors.

The plaintiffs, some of whom operate Web sites with material on topics including obstetrics, sexual health, visual art and poetry, argued the law would prevent adults from access to constitutionally protected material.

Similar laws have been thrown out in six other states, said attorney Michael Bamberg of New York, who represented the plaintiffs.

"We don't think the law as written violates the Constitution or anybody's constitutional rights," said state Attorney General Henry McMaster, who is reviewing the ruling to see if the state will appeal. "We think it's important in today's society that law enforcement take a strong view on obscenity aimed at children."

Bamberg said the ruling means existing state law on distributing material harmful to minors cannot be applied to the Internet.

"The bookstores have been perfectly comfortable with the application of the law in the bookstore context," he said. "When somebody comes up and wants to buy a book you can look at that person and tell if they are 10 years old or a 17-year-old or a 62-year-old."

An amendment to the law four years ago expanded the definition of "material harmful to minors" to include "digital electronic files or other visual depictions or representations."

The suit was brought before any cases were prosecuted under the provision.

"We are pleased to have site operators to make sure minors don't visit their pages. The state suggested operators could verify the age of visitors or put warning labels on Web pages.

But the courts "have explicitly rejected" such methods because they are ineffective, burdensome and "chill adults' ability to engage in, and garner access to, protected speech," Duffy wrote.

Age verification generally requires credit cards but some adults don't have them while some minors do. Internet filters, applied at computers by parents or guardians, are equally effective and less restrictive, the ruling noted.

McMaster disagreed.

"The threat of criminal prosecution is a stronger deterrent than filters and warnings. People can get around filters and warnings," he said. "They don't work and that's why we believe the law is a good law."

But Duffy wrote that while the law fails on the First Amendment challenge, it also represents "an undue burden on interstate commerce" by regulating commerce occurring outside South Carolina.