The case was argued before the high court in April, and a ruling is expected by the end of June. Based partly on skeptical questions posed by justices during the hearing, legal experts expect that the court likely will uphold Arizona's requirement that police check the immigration status of people they stop for other reasons; that provision was put on hold by a judge in July 2010 and hasn't yet been enforced. Less controversial parts of the law were allowed to take effect.

A decision in favor of Arizona could clear the way for other states to enforce immigration-check requirements and create an opening for states to take a larger role in immigration enforcement after mostly staying out of it for decades and letting the federal government handle it alone.

Five others states — Alabama, Georgia, Indiana, South Carolina and Utah — have enacted similar laws.