WASHINGTON -- U.S. Supreme Court justices voiced some skepticism on Monday about an Arizona law that requires people registering to vote in federal elections to show proof of citizenship.
The legal question before the nine justices is whether the voter registration provision of the 2004 state law, known as Proposition 200, is trumped by a federal law, the 1993 National Voter Registration Act, which requires prospective voters to provide one of several possible forms of identification, such as a driver's license number or passport.
The federal law requires no proof of citizenship. Would-be voters simply sign a statement saying they are citizens.
Based on Monday's oral argument, it was unclear how the court will rule but a number of justices, including regular swing vote Justice Anthony Kennedy raised some concerns about the law. A ruling is expected by the end of June.
Several justices said the basic registration form required under the federal law was intended to make registering to vote relatively straightforward. Kennedy said the "whole utility" of having one registration form is lost if it is made too complicated by states requiring additional information.
Justice Sonia Sotomayor appeared to agree on that point as she questioned how requiring additional information could be consistent with the objective of simplifying the process.
Justice Elena Kagan said there was a danger that, for prospective voters, the federal form would become "another hoop to jump through."
The role of the U.S. Election Assistance Commission, a federal agency that oversees changes to state voter registration procedures, loomed large during the argument.
The commission rejected the Arizona plan, prompting several justices to ponder why the state did not file a lawsuit challenging the decision.
Kagan said the EAC "is driving the bus" on such procedure changes, meaning it is "the decision maker with respect to what can be added to the federal form."
In a similar vein, Justice Antonin Scalia repeatedly told Arizona Attorney General Thomas Horne that the state should have filed a lawsuit saying the EAC's decision was unlawful, particularly in light of another case in which Louisiana was granted permission to require additional materials as proof of identification.
"You should have challenged the commission's refusal to place that evidence in the federal form," Scalia said.
Horne, a Republican elected in 2010, responded that he was not in office at the time and did not know why the state did not file a lawsuit.
The case before the high court began instead when state residents, tribal groups and civil rights organizations, including the Inter Tribal Council of Arizona, objected to the law.
Arizona maintains that the federal law does not explicitly pre-empt state voter registration laws and should therefore be allowed to stand. The state's lawyers say the state and federal law are not in conflict and can, in fact, work in unison.
Lawyers for the plaintiffs say the state law is in conflict with the federal law because it conditions acceptance of the federal application form upon compliance with the state's regulations.
Arizona, which shares a border with Mexico, has a reputation for passing tough anti-immigration laws that have brought it into conflict with the Obama administration.
In 2012, the Supreme Court reviewed another of the state's laws. The outcome was mixed. The court upheld a provision that allowed police to ask for immigration papers but struck other parts of the law that, among other things, banned illegal immigrants from soliciting work in public places.
The case is Arizona v. Inter Tribal Council of Arizona, U.S. Supreme Court, No. 12-71.