The case centers on the question of whether federal law preempts provisions of Arizona’s S.B. 1070, which gives Arizona state police the authority detain and check the legal status of anyone who is arrested whom they suspect is an undocumented alien. The Arizona law also makes it a crime for immigrants to be in the state without documentation showing that they are legal.

The law has never gone into effect. Arizona Gov. Jan Brewer, a Republican, signed the bill into law April 2010, but the U.S. government filed suit in federal court before the law went into effect, and both the district court and the U.S. Court of Appeals for the Ninth Circuit said that certain provisions of the law were preempted.

During oral arguments, Dept. of Justice Solicitor General Donald Verrilli, Jr., said that the state provisions could actually hinder federal efforts to enforce the nation’s immigration laws by straining already limited resources: he said federal authorities are most interested in illegal immigrants who break the law, are deported, and then return to the United States. If the law were to go into effect, he said, there could be “mass arrests” and widespread migration of immigrants to neighboring states.

But the justices didn’t seem to be buying Verrilli’s arguments. Justice Antonin Scalia seemed incredulous that under current federal regulatory scheme, “The state has no power to close its borders to people who have no right to be there?”

Even Justice Sonia Sotomayor, an Obama appointee who seemed to want to be sympathetic to the government’s case, told Verrilli at one point that his argument wasn’t “selling very well” among the justices.

Although the case does not directly affect construction employers, a large segment of the construction workforce in Arizona is Hispanic.

Paul Clement, a Washington, D.C., attorney who served as solicitor general during the George W. Bush administration, argued the case for Arizona. The court is expected to issue a ruling in June.