There have been a lot of heated responses to Arizona's law that cracks down on illegal immigrants. Many critics assume that the law would lead to racial profiling--police stopping Hispanics at random and asking them to produce proof that they are here legally. But Byron York points out in the Washington Examiner that the law requires police to check on immigration status only if the person has been stopped "for some legitimate reason" and the police "suspect that he or she might be in the U.S. illegally."
The heart of the law is this provision: "For any lawful contact made by a law enforcement official or a law enforcement agency…where reasonable suspicion exists that the person is an alien who is unlawfully present in the United States, a reasonable attempt shall be made, when practicable, to determine the immigration status of the person…"
Kris Kobach, a University of Missouri Kansas City Law School professor who helped draft the law tells York that "lawful contact" means "the officer is already engaged in some detention of an individual because he's violated some other law. ... The most likely context where this law would come into play is a traffic stop."