The case is known as Republican National Committee v. Mi Familia Vota.

In 2004, Arizona enacted a law which requires new voters to provide documentary proof of citizenship (such as a passport or a birth certificate) when registering to vote in the state. This state law, however, conflicts with a federal law known as the National Voter Registration Act (NVRA), which requires states to register voters who submit a standardized federal registration form.

Previous ruling left it open that NVRA held for only federal elections, not state or local.

The RNC case, which is now before the Supreme Court, concerns a 2022 Arizona law which would impose three new restrictions on these federal-only Arizona voters. It bars them from voting by mail, and from voting for president altogether — thus limiting them to voting only in congressional elections. Additionally, the 2022 law requires the state to reject any new voter registration submitted using the state’s own form if that registration doesn’t include proof of citizenship — even though the state is still required to register that individual as a federal-only voter if the registrant submits the federal form.