WASHINGTON (AP) -- Attorney General Eric Holder said Thursday the Justice Department opened a record number of more than 100 new investigations into possible voting rights discrimination across the country last year.

During an appearance at the National Underground Railroad Freedom Center in Cincinnati, Holder praised the federal government's aggressive enforcement efforts while vowing to defend a landmark voting rights law that is increasingly under attack in this presidential election year.

On Thursday, Holder said that nowhere is the Justice Department's commitment to equal opportunity clearer than in efforts to expand access to voting nationwide.

It was the attorney general's third speech in little more than a month focusing on voting rights, coming amid a flurry of activity by states, largely those controlled by Republicans, to redraw political boundaries and impose requirements that could reduce voting by minorities who enthusiastically supported Barack Obama in the 2008 election.

"The reality is that - in jurisdictions across the country - both overt and subtle forms of discrimination remain all too common - and have not yet been relegated to the pages of history," Holder told the audience.

Pointing to some of the Justice Department's efforts, Holder cited as success stories the cases of two Ohio counties - Cuyahoga and Lorain - which agreed to ensure that bilingual ballots are available on county voting machines and that bilingual poll workers are on hand to help. In another positive outcome, said Holder, a northeast Ohio school board let a federal court determine how to structure elections to give blacks a greater chance of being elected.

In December in Austin, Texas, Holder urged the country to "call on our political parties to resist the temptation to suppress certain votes in the hope of attaining electoral success."

Earlier this month in Columbia, S.C., Holder told thousands of people commemorating the Martin Luther King Jr. holiday that in his travels "I've heard a consistent drumbeat of concern from citizens, who - often for the first time in their lives - now have reason to believe that we are failing to live up to one of our nation's most noble ideals."

Section 5 of the Voting Rights Act requires all or parts of 16 states to obtain advance approval from either the Justice Department's civil rights division or a federal court in Washington before carrying out changes in elections. The states are mostly in the South and all the jurisdictions have a history of discriminating against blacks, American Indians, Asian-Americans, Alaskan Natives or Hispanics.

Despite congressional reauthorization in 2006 of Section 5 for 25 years, its future has come under constitutional challenges in federal courts by Arizona, Florida, Georgia, Shelby County, Ala., and some voters in Kinston, N.C.

As of last week, there were 833 Section 5 submissions for proposed electoral changes awaiting approval at the Justice Department from state, county and local units of government.

In one Section 5 action, the civil rights division in December rejected a new South Carolina law that requires voters to present a photo ID when they go to the polls. It was the first time in nearly two decades the Justice Department had reached such a conclusion about a voter ID law.

A pending Section 5 review involves Texas, where the Justice Department has raised questions over a new photo ID requirement. The state reacted by taking its case for the new law to a federal appeals court in Washington, D.C., where lawyers from the Justice Department and the state will square off. The Justice Department's civil rights division also is immersed in a court battle with Texas over allegedly discriminatory boundaries drawn by the Republican-controlled Texas Legislature and signed into law by Republican Gov. Rick Perry.

The challenges to Section 5's constitutionality followed a 2009 Supreme Court opinion by Chief Justice John Roberts which seemed to raise doubts about whether the provision was still needed.

Section 5 "imposes current burdens and must be justified by current needs," Roberts wrote. "Today, the registration gap between white and black voters is in single digits" in the states covered by the act's preclearance provision and "in some of those states, blacks now register and vote at higher rates than whites."

The stakes would be enormous if the Supreme Court got involved.

In 2006, Congress held hearings and created a 15,000-page record to justify renewing Section 5. Congress found that the Justice Department protected the interests of some 663,503 minority voters from 2000 to May 2006 by refusing to approve changes in political boundaries drawn by states, counties and local units of government. The Justice Department filed over 700 objections to proposed voting changes from 1982 to 2006 in states and counties covered by Section 5. From 1982 to 2003, states and local entities withdrew more than 200 proposed voting changes when the Justice Department started asking questions about them.

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