Kansas Secretary of State Kris Kobach faces a lawsuit aimed at blocking him from imposing a new registration policy as he attempts to enforce a proof-of-citizenship law.

The lawsuit was filed Thursday in Shawnee County District Court by the American Civil Liberties Union on behalf of the gay-rights group Equality Kansas and two prospective voters.

It seeks to prevent Kobach from creating a "dual" registration system under which some voters could cast ballots only in federal races.

The different treatment would apply to people using a national registration form, which doesn’t require proof of citizenship. People using a Kansas form could vote in any race by providing a birth certificate, passport or other papers.

Kobach has said Kansas could be forced to adopt such a system.