In this file photo from November 2014, Kansas Secretary of State Kris Kobach testifies during a meeting of a legislative study committee on election issues.

Topeka ? The American Civil Liberties Union of Kansas filed a new lawsuit in Shawnee County District Court Tuesday seeking to block Secretary of State Kris Kobach’s new regulation that says certain voters who have not provided proof of U.S. citizenship may vote only in federal elections.

That new temporary regulation was approved last week, with little public notice, on the final day for voters to register in time for the upcoming Aug. 2 primaries.

The temporary rule affects an estimated 17,000 voters who either registered through a local motor vehicle office or by submitting a federal mail-in registration form but did not provide proof of U.S. citizenship.

Kobach’s office proposed the rule in response to a recent federal court order saying the state must register those applicants, at least for voting in federal elections.

In the suit, the ACLU argues that the Kansas Legislature has never enacted a statute authorizing the secretary of state to make such a regulation, and that the regulation violates the Kansas Constitution’s guarantee of equal protection.

The lawsuit names three individual plaintiffs, Marvin and Joann Brown of Lenexa, and Charles “Tad” Stricker of Wichita, but it also asks the court to certify the case as a class action suit on behalf of all voters affected by the temporary order.

Shawnee County Judge Franklin Theis ruled in another case earlier this year that Kobach has no legal or regulatory authority during the 2014 elections to conduct a “dual” registration system in which certain voters may vote only in federal elections. But Theis did not issue an order specifically blocking Kobach from conducting such a system in the future. Kobach has appealed that decision to the Kansas Court of Appeals, which has not yet set a date for arguments.

In most states, and under federal law, voters only need to attest, under penalty of perjury, on the registration form that they are U.S. citizens who are eligible to vote. But in Kansas and a handful of other states, they must show documentary proof of U.S. citizenship, either with a birth certificate, passport or other document listed as acceptable under the law.

In May, U.S. District Judge Julie Robinson ruled that the state’s law conflicts with the National Voter Registration Act, at least as it concerns federal elections, and she ordered the state to immediately register an estimated 17,000 voters who had signed up through their motor vehicle offices. The 10th U.S. Circuit Court of Appeals later declined to stay that decision.

As a result, Kobach enacted the new rule that says those voters will have to cast provisional ballots on Election Day, and county officials may count only the votes they cast in federal races, not in state or local elections.

The suit was filed Tuesday, exactly two weeks before the Aug. 2 primaries. But Doug Bonney, legal director for the ACLU of Kansas, noted that advance voting has already started, and he hopes the court will hold an initial hearing soon and rule on the motion for a temporary restraining order before Election Day.

“This is the latest frivolous ACLU lawsuit attempting to knock down our proof of citizenship law,” Kobach said in an email response to the lawsuit. “The ACLU ignores the fact that Kansas law clearly provides the Secretary of State’s office with the authority to issue the regulation in question. The ACLU also ignores the fact that the regulation was issued in order to comply with a federal court order.”

The case was assigned to Shawnee County District Judge Larry Hendricks. As of Tuesday afternoon, no hearing date had been set.