KANSAS CITY, Kan. (Reuters) - The American Civil Liberties Union asked a federal judge on Thursday to block a Kansas state law that requires people to prove American citizenship if they want to register to vote while applying for a driver’s license.

Stickers are seen on a table at a polling stations for the Wisconsin presidential primary election in Milwaukee, Wisconsin, United States, April 5, 2016. REUTERS/Jim Young

U.S. District Court Judge Julie Robinson conducted a four-hour hearing in Kansas City, Kansas, but took no immediate action on the request for a preliminary injunction, pending the outcome of a lawsuit the civil rights group filed in February. The ACLU hopes for a ruling before August and November elections.

The ACLU says Kansas is making illegal demands for additional proof of citizenship, violating the so-called Motor-Voter Law that Congress passed in 1993 to boost voter registration for federal elections by allowing voters to register at state motor vehicle departments.

The Kansas law requiring documents like a birth certificate or U.S. passport for voter registration, which took effect Jan. 1, 2013, is one of numerous voter ID laws passed by Republican-led state legislatures in recent years. The ACLU alleges that Kansas goes beyond what is required by federal law.

Democrats have argued voter ID laws typically hurt potential Democratic supporters like young people and minorities.

Driver’s license applicants should only be required to sign a sworn statement that they are citizens in order to register to vote, ACLU lawyer Dale Ho said in court.

“These are not minor barriers for our clients, they are significant,” Ho said, referring to the requirement to prove citizenship.

Proponents say the laws are intended to curb voter fraud.

“Every time an illegal alien votes it cancels out the vote of an American citizen,” Kansas Secretary of State Kris Kobach, a defendant in the case, told the court.

Kobach said documents such as an affidavit from a relative would be acceptable proof of citizenship.

But Judge Robinson alluded several times to documentation requests being a hardship on some people.

“You’re demanding a level of sophistication that some people just don’t have,” Robinson said. “It seems like a lot of work for the population we are talking about.”

Ho said at least 16,000 people had their applications to register canceled or suspended in Kansas after applying for or renewing a driver’s license. Six of them are plaintiffs in the lawsuit.

Georgia and Alabama passed laws similar to that in Kansas but are not enforcing them, Ho said. Arizona uses the law, but people have not reported as many registration denials as in Kansas.