Jacob Sullum

In 1941, the Supreme Court overturned a Pennsylvania law that required non-citizens to register with the state, carry an "alien identification card" and present it to police officers upon demand.

The court said the law conflicted with a federal policy, based on treaty obligations and the constitutional principle of equal protection, that sought to "protect the personal liberties of law-abiding aliens" and keep them "free from the possibility of inquisitorial practices and police surveillance," including "indiscriminate and repeated interception and interrogation by public officials."

U.S. District Judge Susan Bolton cited that decision last week when she issued a preliminary injunction that prevents Arizona from enforcing major provisions of its new immigration law. Although Arizona did not create its own alien registry, its avowed aim of preventing "the unlawful entry and presence of aliens" can be accomplished only by imposing the sort of "distinct, unusual and extraordinary burdens" that troubled the Supreme Court in 1941.

Under one of the provisions that Bolton blocked, police officers who encounter someone they think might be in the country illegally are required to make "a reasonable attempt" to determine his immigration status. This obligation is triggered by "any lawful stop, detention or arrest," including those associated with trivial offenses such as jaywalking, failing to leash your dog and biking on a sidewalk.

If the suspect is from one of the 36 nations whose citizens are allowed to visit the U.S. for up to 90 days without a visa -- Spain, say -- the police can look at his passport to verify his citizenship and see when he entered the country.

But those two facts do not necessarily show he is lawfully present in the United States, since the Visa Waiver Program imposes various other requirements: Participants are not allowed to study, work or represent a foreign news organization in the U.S., and they may not fall into any of several banned categories, including drug addicts, people with communicable diseases and people with "physical or mental disorders" that pose a danger to themselves or others.

Still, maybe looking at a passport counts as a "reasonable attempt." If an arrest occurs, however, the law says "the person's immigration status" must be "determined before the person is released." That requires checking with Immigration and Customs Enforcement -- although even ICE's records are not conclusive, since they may be based on misinformation about an individual's background or plans.

Jacob Sullum

Jacob Sullum is a senior editor at Reason magazine and a contributing columnist on Townhall.com.
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