Who gets to decide how congressional elections are conducted? It’s a question that should concern every American voter.

Article 1 of the U.S. Constitution says each state may draft its own rules for conducting federal elections, but in case of disagreements, Congress has ultimate authority. The state of Arizona disagrees.

The Supreme Court will soon issue its decision in a case that asks the justices to settle this question: Does the Constitution really mean what it says?

The case at issue is called Arizona v. ITCA. A little background is in order.

Congress enacted the National Voter Registration Act in 1993 to help increase voter participation in federal elections. It was popularly known as the “motor voter” law, for the provision requiring states to offer voter registration when residents apply for or renew their driver’s licenses.

The NVRA also created a standardized, national mail-in registration form. States could still use their own voter registration forms, but they also had to accept and use the federal form for registering voters in federal elections.

Which brings us to Arizona. In 2004, the state passed a voter initiative measure, Proposition 200, intended to “discourage illegal immigration.” Among its provisions, the Arizona law requires voting officials to “reject any application for registration” unless it includes documentation from a list that Arizona says proves U.S. citizenship. The law requires many voter registrants to send in copies of their birth certificates, passports or other sensitive personal documents.

The federal registration postcard also tells would-be voters that they must be U.S. citizens. It reminds them that it is a crime to falsely claim citizenship. And it requires them to sign a statement attesting — under penalty of perjury — that they meet all legal requirements for voter registration, including citizenship.

Congress specifically considered, and rejected, allowing states to require additional documentation of U.S. citizenship along with the federal form, precisely because it made registration too cumbersome and thus undermined the central purpose of the NVRA.

But that’s not good enough for Arizona. It steadfastly refuses to accept the federal voter registration form, or a similar form prepared by the Department of Defense for voter registration by military personnel, unless the federal forms are accompanied by the extra documentation required under Arizona state law.

The results? The district court determined that in a two-year period, Arizona denied voter registration to 31,500 applicants for failing to provide the additional documentation. In Maricopa County alone (which includes Phoenix), community voter registration plummeted by 44 percent. Meanwhile, the state has been unable to produce even one case of a non-citizen attempting to register to vote with the federal postcard form.

In fact, ironically, the great majority of the rejected voters are neither immigrants nor Latinos. Proposition 200 burdens all voter registrants, most of whom in Arizona are native-born and Anglo.

After considering all these facts, the 9th Circuit Court of Appeals concluded that Proposition 200’s additional paperwork requirements are in fact superseded by the NVRA. Their decision was not closely divided; eight of the 10 judges on the panel agreed.

The Supreme Court heard oral arguments in the consolidated case on March 18 and is expected to issue its decision shortly. For the sake of our democracy, let’s hope they reach the same conclusion.

Nina Perales is vice president of litigation for the Mexican American Legal Defense and Educational Fund, which represents individuals who were rejected for voter registration under Proposition 200.