The League of Women Voters sued on Thursday to block a new Wisconsin law requiring voters to present identification such as a drivers license at polling places, saying it would disenfranchise eligible voters.
The lawsuit, filed in Dane County Circuit Court, argues the state constitution allows only convicted felons and the mentally incompetent to be excluded from voting.
The new law creates a third class of people, those who do not have ID, said Andrea Kaminski, Wisconsin League of Women Voters Executive Director. Critics of the law say it would mainly affect minorities and the elderly, who may not have ID.
The law requires voters to present identification, such as a drivers license or a passport, when they cast ballots in federal, state and local elections. The measure, passed by the Republican-controlled state legislature, takes effect next year, in time for the November general election.
Wisconsin Governor Scott Walker said the law would ensure the "integrity" of elections.
Thirty states now require voters to show some form of ID before voting, according to the National Council of State Legislatures website. In 14 of those, including Wisconsin, the ID must include a photo of the voter.
Advocates of the laws, which have passed this year in Alabama, Kansas, Rhode Island, South Carolina, Tennessee and Texas, say they are needed to combat voter fraud. Opponents say there is no evidence of widespread fraud.
So far efforts to overturn the laws have been unsuccessful. Indiana's law was initially blocked but reinstated by higher courts. Arizona, Georgia and Michigan laws have been upheld in court. A challenge to Oklahoma's law is pending.
The Wisconsin voter ID law was part of an ambitious agenda championed by Walker this year, also including curbs on the power of public unions, spending cuts and easing restrictions on concealed weapons.
A Milwaukee resident, Adib Khatib Timbuktu, has challenged the law in federal court, saying it violates the equal protection guarantees of the U.S. Constitution.
Jennie Bowser, a senior fellow at the council of state legislatures, said she expects the number of challenges nationwide to grow following the November, 2012 elections.
"I think opponents of voter ID will be out in force in the states with the new strict laws looking for people who can't vote because of lack of ID and who might be willing to be plaintiffs in a legal challenge," she said.
(Editing by Greg McCune)