Republican Attorney General J.B. Van Hollen filed the appeal with the 7th U.S. Circuit Court of Appeals on Monday.
Last month U.S. District Judge Lynn Adelman ruled that Wisconsin's law requiring voters show a state-issued photo ID at the polls imposes an unfair burden on poor and minority voters and violates the U.S. Constitution's guarantee of equal protection.
Two separate cases challenging the Republican-backed law are also pending before the Wisconsin Supreme Court. Van Hollen would have to win all of the cases in order for the law to be in effect for the November elections.
Van Hollen also asked Adelman to stay his ruling while the appeal is pending.