A U.S. appeals court upheld an Internet gambling ban Tuesday, rejecting a challenge from an association of off-shore bookies that the federal prohibition was too vague and violated privacy rights.

The 3rd U.S. Circuit Court of Appeals in Philadelphia rejected arguments from Interactive Media Entertainment & Gaming Association in New Jersey, which had filed the lawsuit hoping to legalize online betting in that state.

Congress passed the Unlawful Internet Gambling Enforcement Act in 2006 to ban online gambling that would be illegal in the state where the individual or gambling business conducts the transaction. The law does not target the bet itself but criminalizes bank or credit card transactions linked to the bet.

The group, comprised of mostly offshore betting operators, had attacked the law as unconstitutionally vague. Their lawyers questioned how the location of an online bet would be determined if the gambler is in Delaware, for instance, and the operation is in Costa Rica.

At least one of the three judges who heard arguments last month seemed to question that logic.

"No matter how metaphysical you want to get, I'm not in Costa Rica, I'm in Delaware," 3rd Circuit Judge Kent Jordan said.

The court also rejected arguments that the law invades a gambler's right to privacy in the home.

The Justice Department, which successfully defended the law, had no immediate comment, a spokesman said.