In the first of Arizona's recently enacted laws aimed at curbing illegal immigration the Supreme Court supported the rights of states to pass laws such as the Legal Arizona Workers Act which withdraws licensing from businesses that employ illegals.
The opinion, written by Chief Justice Roberts, turned on whether the Arizona law is a "licensing law" that escapes the federal preemption doctrine.
The case is Chamber of Commerce, et al. v. Whiting, et al.
Another Arizona law, one that gives police the authority to detain and arrest anyone suspected of being an unlawful alien, is working it's way to the Supreme Court.
Andrew Cohen writes about all of it here.