WASHINGTON — The Supreme Court appeared divided along familiar lines on Monday as it heard arguments over whether Arizona can require proof of citizenship from people seeking to register to vote in federal elections.
Several of the court’s more liberal justices sounded doubtful about a state law that imposes requirements beyond those listed in a federal law.
“Many people don’t have the documents that Arizona requires,’’ Justice Sonia Sotomayor said.
The Arizona law, enacted in 2004 by a ballot initiative, requires prospective voters to prove that they are citizens by submitting copies of or information concerning various documents, including birth certificates, passports, naturalization papers, or Arizona driver’s licenses, which are available only to people who are in the state lawfully.
The question for the justices was whether that state law conflicted with the National Voter Registration Act of 1993, which allows voters to register using a federal form that asks, ‘‘Are you a citizen of the United States?’’
Prospective voters must check a box yes or no, and they must sign the form, swearing that they are citizens, under penalty of perjury.
Several members of the court’s conservative wing indicated that the state was free to impose additional requirements to make sure only citizens vote.
Justice Antonin Scalia said the federal form was inadequate. ‘‘So it’s under oath,’’ he said. ‘‘Big deal. If you’re willing to violate the voting laws, I suppose you’re willing to violate the perjury laws.
‘‘Under oath,’’ he added, ‘‘is not proof at all. It’s just a statement.’’
Although the case heard Monday focuses on Arizona, it has broader implications because four other states — Alabama, Georgia, Kansas, and Tennessee — have similar requirements, and 12 other states are contemplating such legislation.
This is the second voting eligibility issue the high court is tackling this session. Last month, several justices voiced skepticism about whether a section of the Voting Rights Act of 1965, a law that has helped millions of minorities exercise their right to vote, especially in areas of the Deep South, was still needed.
The court will issue rulings in both cases later this year.
Patricia A. Millett, a lawyer for several groups challenging the Arizona law, responded that ‘‘statements under oath in criminal cases are proof beyond a reasonable doubt’’ sufficient to lead to the death penalty.
She added that tens of thousands of people had been rejected from the registration rolls thanks to the Arizona law, though there was no evidence that they were not citizens.
The Appeals Court for the Ninth Circuit, in San Francisco, blocked the state law last year, saying it conflicted with the federal one.
That decision, from a 10-judge panel, affirmed a 2010 ruling from a three-judge panel that included Justice Sandra Day O’Connor, who retired from the Supreme Court in 2006 but occasionally acts as a visiting appeals court judge.
O’Connor, who was in the courtroom on Monday, joined the majority in 2010 in ruling that the state law was inconsistent with the federal one and so could not survive.
Justice Anthony M. Kennedy, who may hold the decisive vote, asked questions on Monday sympathetic to both sides.
Under Arizona’s interpretation, he said, ‘‘it seems to me the federal form, as some of my colleagues have indicated, is not worth very much.’’ Later, though, he said the appeals court had not given enough weight to Arizona’s concerns.
‘‘The state has a very strong and vital interest in the integrity of its elections,’’ he said, ‘‘even when those, and perhaps especially when those, are elections of federal officials.’’
Thomas C. Horne, Arizona’s attorney general, said the federal approach was insufficient to protect the integrity of federal elections in his state.
‘‘It’s essentially an honor system,’’ he said of the statement required by the federal form. ‘‘It does not do the job.’’
Horne said Arizona should be free to supplement the federal form even though the federal law required state officials to ‘‘accept and use’’ the federal form. An airline may ‘‘accept and use’’ an electronic ticket, he said, and yet still require identification.
Justice Elena Kagan said that was the wrong analogy. Arizona’s system is akin, she said, to requiring a paper ticket in addition to the electronic one. ‘‘That would be inconsistent with the ‘accept and use’ language,’’ she said.
Though Scalia appeared attentive to the state’s concerns, he suggested that it may have fumbled the litigation by not going to court after losing before the federal Election Assistance Commission.
“You should have challenged the commission’s refusal to place that evidence in the federal form,’’ Scalia told Horne.