A part of Arizona's law on illegal immigration was struck down by the 9th U.S. Circuit Court of Appeals Tuesday, which upheld a Phoenix federal judge in the case.
The three-judge panel said the "harboring and transporting of illegal aliens" clause of SB 1070 was a violation of due process and because federal law preempts it.
Its opinion said the law's description of "being in violation of a criminal offense" was vague and "unintelligible."
The U.S. Supreme Court last year ruled on four parts of SB 1070, striking down three and upholding one, which supporters said was the key provision, allowing law-enforcement officers to stop and question people suspected of being in the country illegally.
The case decided Tuesday came from a lawsuit filed by a coalition of immigrant support groups, unions, religious organizations and individuals. U.S. District Judge Susan Bolton of Phoenix decided on the original case, issuing an injunction to stop enforcement of the provision.
SB 1070, passed by the Arizona Legislature and signed by Gov. Jan Brewer in 2010, was considered the toughest anti-immigration law in the nation at the time. Large sections of it have subsequently been challenged in court.
The law came about from a push to stop illegal immigration in the state on several fronts. The part struck down Tuesday would have made it a crime to transport people in the country illegally, to "conceal, harbor or shield" them or to induce them to reside in Arizona.