DENVER (AP) — Kansas is asking a federal appeals court to keep thousands of people who haven’t yet provided the documents to prove they are U.S. citizens from voting in November’s election.

Judges from the 10th U.S. Circuit Court of Appeals in Denver are set to hear arguments Tuesday in the legal fight over how the state enforces its proof-of-citizenship requirement for voters who register at motor vehicle offices.

Since 1993, states must allow people to register to vote when they apply for or renew their driver’s licenses. The so-called motor-voter law says that people can only be asked for “minimal information” when registering to vote, allowing them to simply affirm they are citizens.

A federal judge in May temporarily blocked Kansas from disenfranchising about 18,000 who registered to vote at motor vehicle offices without providing citizenship paperwork such as birth certificates or naturalization papers. U.S. District Judge Julie Robinson ordered the state to register them for federal elections until the case, one of at least four the state is facing over its law, is decided at trial. The state has said that ruling could affect as many as 50,000 potential voters by the November elections.

Kansas Secretary of State Kris Kobach wants the appeals court to overturn her preliminary order.

In the appeal, Kobach, a national leader in Republican voting requirement efforts, argued that the motor voter law doesn’t bar states from asking for proof of citizenship and that it doesn’t make sense to hold people who register to vote elsewhere in the state to a higher standard than those who apply to register at motor vehicle offices.

The American Civil Liberties Union sued on behalf of the League of Women Voters and people whose registrations were held up because the state said they were incomplete.

Kobach has championed the documentation requirement as a way to prevent non-citizens from voting, particularly immigrants who are in the U.S. illegally. Critics contend the requirement suppresses turnout.

Robinson said evidence in the case shows only three instances in Kansas where noncitizens voted in a federal election between 1995 and 2013, and about 14 noncitizens attempted to register during that time. Robinson said the number of people disenfranchised outweighed the harm of those cases.

While people getting new licenses are asked to show proof that they are in the country legally, the ACLU says clerks in motor vehicle offices don’t always tell people seeking license renewals that they need to provide documents proving their U.S. citizenship to register to vote and that many leave the motor vehicle office mistakenly believing they are registered. Some of the people the ACLU represents said they later got postcards notifying them that they had to provide proof of citizenship, but one man went to the polls on election day only to find out he wasn’t registered.

Alabama, Arizona and Georgia have similar registration requirements on the books, but Alabama and Georgia are not currently enforcing them. Arizona does not require additional citizenship papers from people registering at motor vehicle offices beyond what’s required to get a driver’s license.