TOPEKA, Kan. — Kansas Secretary of State Kris Kobach was sued Thursday by people seeking to block him from imposing a dual voter registration policy as part of the state’s proof-of-citizenship law.

But Kobach said that while his office has done some planning for such a system, he’s trying to avoid creating it.

The American Civil Liberties Union filed the lawsuit in Shawnee County District Court on behalf of Equality Kansas, the state’s leading gay rights group, and prospective voters Aaron Belenky of Overland Park and Scott Jones of Lawrence. It seeks to prevent Kobachfrom creating a registration system in which some voters are eligible to cast ballots only in presidential, U.S. Senate and congressional races, while others can cast ballots in all races.

The different treatment would be based on whether the prospective voter uses a national registration form — which requires only that someone sign a statement that he or she is a U.S. citizen — without complying with the state’s additional requirement to present a birth certificate, passport or other citizenship papers. People using a Kansas form could vote in all races, but only if they complied with the proof-of-citizenship requirement, which took effect in January.

Kobach said Kansas will be forced to adopt a dual registration system if the federal government does not modify the national registration form to help Kansas enforce its proof-of-citizenship rule. He’s engaged in a separate legal battle to force federal officials to change the national form.

“We have not implemented any two-tiered election system,” Kobach said. “We have merely laid contingency plans.”

But the lawsuit said Kobach already has imposed the new policy on his own through a directive this summer to county election officials and that his actions violate voters’ right to equal legal protection under the state constitution.

“There’s nothing in the statute to give him the authority — or any state agency the authority — to just make stuff up,” Tom Witt, Equality Kansas’ executive director, said in an interview. “This is just over the top, egregious, clearly illegal and probably unconstitutional.”

Arizona also has a proof-of-citizenship requirement, and officials there have created a dual registration system. Arizona Secretary of State Ken Bennett has joined Kobach in the effort to force a change in the national registration form.

Meanwhile, the registrations of nearly 17,700 prospective Kansas voters were on hold as of this week because they had yet to comply with the proof-of-citizenship rule.

Belenky was unable to vote in a local election in Overland Park in October, according to the lawsuit, though he filled out the national registration form in early August. Equality Kansas argues that its ability to conduct voter registration drives is hindered.

The lawsuit alleges that Kobach, a Republican who championed the proof-of-citizenship law as an anti-fraud measure, has improperly imposed “an entirely new” registration system unilaterally and likened the policy to one enacted in Mississippi in 1890 to keep blacks from voting.

Doug Bonney, chief counsel for the ACLU of Kansas and Western Missouri, said the dual registration system creates “second-class citizens.”

The lawsuit also names Brad Bryant, the secretary of state’s elections director, as a defendant. Bryant sent county election officials a July 30 memo telling them they must track who registers using the federal form and that those people can vote only in federal races until they produce citizenship documents. The memo is an exhibit in the lawsuit.

Kobach has said himself that creating a dual registration system in Kansas would be burdensome. In August, he, Bennett and their states filed a federal lawsuit against the U.S. Election Assistance Commission in an attempt to force the federal agency to modify the national registration form so that Arizona and Kansas voters using the form must comply with the states’ proof-of-citizenship requirements.

The move came two months after the U.S. Supreme Court reviewed Arizona’s law and said it couldn’t refuse to accept the national registration form.

A hearing on the states’ request for a temporary injunction forcing a modification of the national form is scheduled for Dec. 13 in Topeka.

Bonney said the constitutionality of the Kansas proof-of-citizenship law already is an issue in the two states’ federal lawsuit, while Kobach’s creation of a dual registration system is “the immediate problem.”

But Kobach said that Kansas will avoid having a dual registration system if it and Arizona prevail in their federal lawsuit.

“In all likelihood this (new state court) case will be moot in several months,” Kobach said.