WASHINGTON - The Obama administration's civil-rights office stepped up its fight with Southern states over voting rights, saying Friday that it would block a new South Carolina law that requires voters to show a government-issued photo ID before casting a ballot.

The Justice Department invoked the Voting Rights Act, saying the new photo ID rule could deny the right to vote for tens of thousands of blacks and other minorities.

"According to the state's statistics, there are 81,938 minority citizens who are already registered to vote and who lack DMV-issued identification," Thomas E. Perez, chief of Justice's Civil Rights Division, said in a letter to South Carolina officials. He referred to a state-issued driver's license, the most common form of photo ID.

Under current law, a South Carolina resident who is registered to vote may cast a ballot if he or she has a voter registration card and a signature on the polling list, Perez said.

South Carolina was one of a number of states to enact new laws this year that tighten the rules for voting. Last week, Attorney General Eric H. Holder Jr. spoke out against these laws, describing them in the words of Rep. John Lewis (D., Ga.) as "a deliberate and systematic attempt" to prevent millions of elderly, low-income and minority Americans from voting.

Under the Section 5 of the Voting Rights Act, Southern states with a history of racial discrimination must seek advance approval from Justice or a federal court before adopting new election laws.

South Carolina Gov. Nikki Haley vowed to get the Justice decision overturned, saying in a statement: "It is outrageous, and we plan to look at every possible option to get this terrible, clearly political decision overturned so we can protect the integrity of our electoral process and our 10th Amendment rights."

Still under review are new election laws from several other Southern states, including Texas and Florida.

Republicans say that photo ID requirements would help prevent fraudulent votes. Democrats say there is virtually no evidence that imposters try to show up and claim to be a registered voter.