A federal appeals court seems likely to side with voting rights groups trying to stop Kansas, Georgia and Alabama from making residents prove they are U.S. citizens when registering to vote using a national form.

Judges heard arguments in the case Thursday. At issue is whether to overturn a decision by a U.S. election official who changed the form's proof-of-citizenship requirements at the behest of the three states, without public notice.

People registering to vote in other states need only to swear that they are citizens, not show proof.

Two of the three judges hearing the case suggested the citizenship requirement can pose a tough hurdle for many eligible voters.

A federal judge in July refused to block the requirement while the case is being decided.