Topeka ? Kansas Secretary of State Kris Kobach will ask a federal appeals court panel on Tuesday to reverse a lower court decision that would block the state from enforcing part of its law requiring voters to show proof of U.S. citizenship in order to register.

A three-judge panel of the 10th U.S. Circuit Court of Appeals will hear oral arguments Tuesday in Denver in a case that affects an estimated 17,500 voters who signed up when they renewed their driver’s licenses at local motor vehicle offices.

The American Civil Liberties Union of Kansas filed the case in February, arguing that the state law conflicts with part of the National Voter Registration Act, commonly known as the federal “motor voter” law.

Among other things, that law requires voter registration to be available at all driver’s license offices, and it only requires that voters attest, under penalty of perjury, that they are U.S. citizens.

In May, U.S. District Judge Julie Robinson granted a preliminary injunction requiring the state to register all voters who had used that option since the law took effect in 2013 and allow them to vote, at least in federal races, during the 2016 election cycle.

That injunction is set to stay in force until the court conducts a full trial in the lawsuit, which is currently set for May 2017.

After the 10th Circuit refused to issue a stay of that order pending appeal, Kobach enacted new regulations that effectively set up a dual registration system in which those voters who had registered at motor vehicle offices without showing proof of citizenship would have to cast provisional ballots, and only their votes in federal races would be counted.

But in a hastily filed case in state court, a Shawnee County judge issued another order just days before the Aug. 2 primary temporarily blocking that regulation from being enforced.

That enabled those affected voters to cast full ballots in the primary races. After the election, however, county election officers reported that only a handful of such voters actually took advantage of the rulings by voting in the primary.

Kobach has argued that the injunctions put administrative burdens on his agency, and on county election offices, and that they create confusion on Election Day over who is allowed to vote and who is not.

Kobach lobbied for passage of the law in 2011, immediately after taking office, saying it is needed to prevent non-U.S. citizens from voting in Kansas elections.

But the ACLU argues that there have only been a few rare cases of noncitizens voting in U.S. elections, and that those cases do not justify blocking tens of thousands of legally qualified citizens from voting, simply because they cannot produce a birth certificate, passport or other form of documentation.

Doug Bonney, an attorney for the ACLU, said the 10th Circuit has not yet indicated how soon it will rule on the appeal. But he said he expects a ruling well in advance of the Nov. 8 general elections.