MILWAUKEE — A federal judge struck down Wisconsin’s voter identification law Tuesday, declaring that a requirement that voters show a state-issued photo ID at the polls imposes an unfair burden on poor and minority voters.
US District Judge Lynn Adelman sided with opponents of the law, who argued that low-income and minority voters are not as likely to have photo IDs or the documents needed to get them.
Adelman said the law violated the Constitution’s guarantee of equal protection. He also said the law appeared too flawed to fix with legislative amendments.
Adelman’s decision invalidates Wisconsin’s law and means voter ID probably will not be in place for the fall elections, when Governor Scott Walker, a Republican, faces reelection.
Although Walker committed last month to calling a special legislative session if the law were struck down in court, his spokeswoman would not commit to that Tuesday.
‘‘We believe the voter ID law is constitutional and will ultimately be upheld,’’ Walker spokeswoman Laurel Patrick said in an e-mail. ‘‘We’re reviewing the decision for any potential action.’’
The ruling could set a precedent for similar legal challenges in Texas, North Carolina, and elsewhere.
There are 31 states with laws in effect requiring voters to show some form of identification, according to the National Conference of State Legislatures.
Seven states have strict photo ID requirements similar to the one a state judge struck down in Arkansas last week; that decision has been appealed to the Arkansas Supreme Court. Pennsylvania’s voter ID law has been put on hold because of court challenges.
This month, President Obama waded into the voter ID debate, accusing Republicans of using restrictions to keep voters from the polls and jeopardizing 50 years of expanded voting access for millions of black Americans and other minorities.
A Dane County judge had already blocked Wisconsin’s law in state court. The state Supreme Court heard arguments in two separate lawsuits in February, although it is not clear when the justices will issue a ruling. For voter ID to be reinstated, the state’s high court would have to rule that it does not violate the state constitution, and Adelman’s decision would have to be overturned on appeal.
Wisconsin’s Department of Justice, which defended the state law in court, pledged to continue the fight.
‘‘I am disappointed with the order and continue to believe Wisconsin’s law is constitutional,’’ Attorney General J.B. Van Hollen said in a statement. ‘‘We will appeal.’’
Republican backers had argued that requiring voters to show ID would cut down on voter fraud and boost public confidence in the integrity of the election process.
But Adelman, who was appointed to the bench in 1997 by President Bill Clinton, said the state failed to prove that voter fraud is a legitimate problem.
Wisconsin’s Republican-led Legislature passed the photo ID requirement in 2011, scoring a long-sought GOP priority. Former governor Jim Doyle, a Democrat, had vetoed a similar requirement three times between 2002 and 2005.
Wisconsin’s law was only in effect for a 2012 primary before a Dane County judge declared it unconstitutional.