A federal judge revived on Wednesday a lawsuit challenging a Kansas law requiring prospective voters to prove they are U.S. citizens, saying the case is of constitutional significance and public interest.

“This case deserves to be decided on the merits and not through procedural default,” wrote U.S. District Judge Julie Robinson.

She gave Kansas Secretary of State Kris Kobach a pass for failing to file a timely response to the lawsuit, saying his negligence in missing the deadline was not willful. She set aside a court clerk’s default judgment issued last week against the state.

At issue is a Kansas law that requires people who register to vote to provide documentary proof of citizenship such as a birth certificate, U.S. passport or naturalization certificate.

Kobach, a conservative Republican, has championed the proof-of-citizenship requirement as an anti-fraud measure that keeps non-citizens from voting, including immigrants living in the U.S. illegally. Critics say such requirements suppress voter turnout, particularly among young and minority voters, and that there have been few cases of fraud in the past.

The lawsuit, filed by prospective voter Parker Bednasek, contends the state’s proof-of-citizenship requirement violates voters’ constitutional right to due legal process and the right to freely travel from state to state by infringing on people’s ability to vote and to sign petitions. It states the actions Kobach has taken to verify citizenship status discriminate against people who were born or got married in other states.

Kobach is facing at least four separate lawsuits challenging various aspects of the law.

Also on Wednesday, the 10th Circuit Court of Appeals issued an 85-page opinion that outlined the legal reasoning behind its decision earlier this month in a separate lawsuit that affected people who registered to vote at motor vehicle offices.

The appeals court essentially explained why it upheld Robinson’s preliminary injunction requiring the state to register thousands of people for federal elections. That case was filed by the American Civil Liberties Union on behalf of several prospective voters and the League of Women Voters.