Michael Newdow, a Sacramento doctor and lawyer, sued the Elk Grove Unified School District in 2000 for forcing public school children to recite the pledge, saying it was unconstitutional.

The 9th U.S. Circuit Court of Appeals ruled in Newdow's favor in 2002, but two years later, the U.S. Supreme Court ruled that Newdow lacked standing to sue because he didn't have custody of the daughter on whose behalf he brought the case. He immediately filed a second lawsuit on behalf of three unidentified parents and their children.

In 2005, a federal judge in Sacramento found in favor of Newdow, ruling the pledge was unconstitutional because its reference to "one nation under God" violates children's rights to be "free from a coercive requirement to affirm God." The judge said he was following the precedent set by the 9th Circuit Court's ruling in Newdow's first case.

A three-judge panel from that court was to hear arguments in the case on Tuesday. The same panel also was to hear arguments in Newdow's case against the national motto, "In God We Trust."

In 2005, Newdow sued Congress and several federal officials, arguing that making money with the motto on it violated the First Amendment clause requiring the separation of church and state.

Last year, a federal judge in Sacramento disagreed, saying the words did not violate Newdow's atheism. Newdow appealed.

Congress first authorized a reference to God on a two-cent piece in 1864. In 1955, the year after lawmakers added the words "under God" to the Pledge of Allegiance, Congress passed a law requiring all U.S. currency to carry the motto "In God We Trust."