A federal lawsuit claims a Louisiana law discriminates against foreign-born, naturalized U.S. citizens by arbitrarily subjecting them to “heightened” voter registration requirements that don’t apply to native-born citizens.

Attorneys from the Southern Poverty Law Center and the Fair Elections Legal Network filed the suit Wednesday against Louisiana Secretary of State Tom Schedler and state Commissioner of Elections Angie Rogers.

The suit claims a state law on the books since 1874 is unconstitutional because it requires naturalized citizens to provide documents proving their citizenship when they register to vote, while other residents must simply swear that they are citizens.

The plaintiffs’ attorneys are seeking a preliminary injunction blocking its enforcement.

The suit says Louisiana’s law appears to be the only one of its kind still enforced in the U.S.

Four other states — Alabama, Arizona, Georgia and Kansas — currently have proof-of-citizenship requirements for voter registration. Jon Sherman, an attorney for the Fair Elections Legal Network, said Louisiana’s law is different from the others because its requirements single out naturalized citizens.