Opponents of the provision of the 2003 federal law that sets a five-year mandatory prison term for promoting child porn have said that movies that depict adolescent sex could fall under the law.
But Solicitor General Paul Clement, the administration's top Supreme Court lawyer, said the law is not meant to cover movies like "Lolita," "Traffic," "American Beauty" or "Titanic."
"If you're taking a movie like 'Traffic' or 'American Beauty' and you're promoting it, you have nothing to worry about with this statute," Clement said.
He asked the court to uphold the law as part of Congress' effort to protect children by eliminating the widespread market in child pornography.
The 11th U.S. Circuit Court of Appeals struck down the provision because it makes a crime out of merely talking about illegal images or possessing innocent materials that someone else might believe is pornography.
In the appeals court's view, the law could apply to an e-mail sent by a grandparent and entitled "Good pics of kids in bed," showing grandchildren dressed in pajamas.
Richard Diaz, the lawyer for a man convicted under the law, told the court, "It captures protected speech about materials that may not even, in fact, exist."
In 2002, the court struck down key provisions of a 1996 child pornography law because they called into question legitimate educational, scientific or artistic depictions of youthful sex.
Congress responded the next year with the PROTECT Act, which contains the provision under challenge in the current case.