WASHINGTON, July 23 (Reuters) - The U.S. Department of Justice is investigating whether Pennsylvania's new voter identification law discriminates against minorities, according to a letter released on Monday.

In a step toward a possible federal lawsuit under the Voting Rights Act, the Justice Department sent a letter to Pennsylvania Secretary of the Commonwealth Carol Aichele asking for data on the state's registered voters.

Passed in 1965 during the peak of the civil rights era, the Voting Rights Act bans rules that make it more difficult for minorities to vote.

The Justice Department will analyze the Pennsylvania data to determine if voters who lack proper ID under the new law are disproportionally black or Hispanic.

Pennsylvania's law will be challenged this week in state court by civil rights groups that say the law makes it too difficult for the general public to vote. If the law is upheld, a federal lawsuit alleging discrimination may follow.

Pennsylvania is one of 11 states to pass voter ID laws since 2010. The Republican-controlled state legislature said requiring voters to present ID at the polls will prevent fraud, while opponents say the law targets minority and elderly voters. The two groups vote mostly Democratic and are less likely to have valid ID.

The Justice Department has brought Voting Rights Act challenges against several other states for their voter ID laws. Lawsuits from Texas and South Carolina are pending. (Reporting by Drew Singer; editing by Kevin Drawbaugh and Mohammad Zargham)