Millions more Americans will be required to show photo identification when they head to the polls in four states in 2012, headlining the welter of new laws across the nation that take effect with the turn of the year.

Kansas, Rhode Island, Tennessee and Texas will require voters to prove their identities at the ballot box, bringing the total number of states that require some form of voter identification to 30, according to the National Conference of State Legislatures, a bipartisan group that provides research and data to state governments.

The voter ID measures are among a large number of new state laws that also reflect concerns related to illegal immigration, employment and the well-being of the country's youth. An estimated 40,000 new laws were passed in 2011, up 29% from the previous year.

"Voter ID was definitely a hot issue, and the debate around it was close to boiling over," says Meagan Dorsch, the NCLS's director of public affairs. "I think that in 2012 we could be looking at a flurry of lawsuits over voter ID laws passed in 2011."

Opponents of such laws say they impose an unfair barrier to those who are less likely to have photo IDs, including the poor and the elderly. In December, the Justice Department blocked a South Carolina voter ID law—saying it would damp turn-out among African-Americans—and is reviewing a similar Texas law.