A judge must consider whether Wisconsin's voter photo identification law applies to people who face daunting obstacles in obtaining identification, a three-judge federal appellate panel ruled Tuesday.

The American Civil Liberties Union and the National Law Center for Homelessness and Poverty filed a federal lawsuit in 2011 challenging the law. U.S. District Judge Lynn Adelman struck the law down in April 2014, saying it unfairly burdens poor and minority voters who may lack such identification.

But a three-judge panel from the 7th Circuit U.S. Court of Appeals ultimately reversed him and upheld the law that October, ruling Wisconsin's law is substantially similar to one in Indiana that the U.S. Supreme Court declared constitutional. The law was in effect for last week's presidential primary.

The ACLU and the national homeless center have continued to argue, however, that voters who face stiff hurdles in getting a photo ID should be allowed to vote by affidavit. They say those voters include people who can't obtain IDs because of name mismatches or other errors in birth certificates or other necessary documents; those who need a credential from another agency such as the Social Security Administration that they can't get without a state photo ID; or those who need a document that no longer exists.