Opponents of the laws point out almost every state legislature that has passed them in the past two years is Republican-controlled and those affected most are minority groups and the urban poor -- constituencies who tend to vote Democratic, The New York Times reported Thursday.
Supporters say the laws protect the integrity of elections, prevent voter fraud and increase public confidence in the electoral process.
The Pennsylvania Department of State estimated this month 759,000 registered voters may be at risk of not having the required identification and said it would send letters to all of them explaining what they needed to do.
"Obama won Pennsylvania in 2008 by 600,000 votes," said Witold Walczak, legal director of the American Civil Liberties Union of Pennsylvania, which is leading a suit challenging the voter-ID law. "What is most galling is to hear the law's proponents argue that one person voting improperly undermines the integrity of the election. What about all the people prevented improperly from voting? Doesn't that undermine the integrity of the election?"
In Pennsylvania, voters must present specific kinds of photo IDs before voting.
"We don't know whether voter fraud is a huge or a small problem, but we believe the new law will preserve the integrity of every vote," said Ronald G. Ruman, spokesman for the Pennsylvania Department of State. "The goal is to make sure that every vote cast counts."
The Obama administration blocked a Texas voter-identification law on racial discrimination grounds, and last week Texas took the Obama administration to court over the law.
Florida officials have successfully sued for access to a federal database of non-citizens with the goal of purging them from voter rolls, and other states plan to do the same, the Times said.
Thirty-three states have passed voter-identification laws. Of these, 15 do not require photo IDs, the National Conference of State Legislatures said.