In a 7–2 decision, the Supreme Court held that Arizona's registration requirements were unlawful because they were preempted by federal voting laws.

"[2] The state law requires, besides other things, persons to provide proof of citizenship to register to vote, and requires voter-registration officials to "reject" any application for registration, including a Federal Form under the National Voter Registration Act of 1993, that is not accompanied by documentary evidence of citizenship.

[3][1] However, in April 2011, the court granted Arizona's petition for en banc review of this ruling, and it heard oral arguments on June 21, 2011.

[6] In July 2012, Arizona petitioned the Supreme Court for a writ of certiorari to review the Ninth Circuit's ruling.

[1] Considered with the text of the House Electors Qualifications Clause of Article I, Section II, the Elections Clause of Article II, Section I, and the 17th Amendment, the Court's concluded that the Elections Clause of Article I, Section IV "empowers Congress to regulate how federal elections are held, but not who may vote in them" and that the holding in Oregon v. Mitchell (1970) on Section 302 of the Voting Rights Act Amendments of 1970 that permitted Congress to preempt state voter qualifications for minimum voting age in federal elections under the Equal Protection Clause was of minimal precedential value to the decision.