WASHINGTON -- President Obama gave a glowing rollout Monday to Thomas Perez, his choice to lead the Labor Department after an aggressive stint as the nation's chief civil rights enforcer. But the nomination quickly ran into trouble as a Republican senator declared he would block the nomination until GOP concerns about Perez's Justice Department tenure are addressed.

Sen. David Vitter said he objects because Perez enforced Louisiana's voting rights laws in a way "that specifically benefits the politics of the president and his administration at the expense of identity security" of registered voters in the state. The Justice Department, he said, has not responded to Vitter's 2011 letter on the subject.

But Obama and his allies pressed ahead with Perez's debut in a new role, in which he would shift from the upper ranks of the Justice Department, saying they expect him to bring the same aggressive mindset to the Labor Department. They predicted he would raise the agency's profile and play a more prominent role in the Cabinet than Hilda Solis, who left the post in January.

Obama called Perez a "consensus builder" whose "story reminds us of this country's promise."

"Tom's made protecting that promise for everybody the cause of his life," Obama said in an appearance with Perez in the White House East Room.

Perez is the only Hispanic so far to be named to Obama's second-term Cabinet.

"Our nation still faces critical economic challenges, and the department's mission is as important as ever," Perez said, sprinkling some Spanish throughout his remarks.

The son of Dominican immigrants who once worked as a garbage collector, Perez has led the Justice Department's Civil Rights Division since 2009. If confirmed by the Senate, he would take over the Labor Department as Obama pushes several worker-oriented initiatives, including an overhaul of immigration laws and an increase in the minimum wage.

But he could face spirited opposition from some Republicans lawmakers who say his tenure at Justice has been guided too much by political ideology. His nomination comes days after a report from the Justice Department's inspector general found the agency's voting rights section has been plagued by ideological divisions and unprofessional conduct over two presidential administrations.

"This is an unfortunate and needlessly divisive nomination," said Sen. Jeff Sessions, R-Ala., who called Perez's views on illegal immigration "far outside the mainstream."

Vitter said Monday he would block Perez's nomination until the Justice Department responded to the 2011 letter, in which Vitter complained about "spotty enforcement" of voting rights laws in Louisiana. Vitter claims the department made registration of welfare recipients a priority while ignoring a duty to remove ineligible voters from the rolls.

Before taking the job as assistant attorney general, the 51-year-old Perez was secretary of Maryland's Department of Labor, Licensing and Regulation, where he vigorously enforced safety and wage violations, pushed through tough new consumer protections against foreclosure, and helped implement the nation's first statewide living wage law.

"I think he will raise the profile of the Labor Department," said Laura Murphy, director of the American Civil Liberty Union's Washington legislative office. "I think he understands that the role of the federal government is to help ensure that the rules of the game are fair."

At Justice, Perez has reinvigorated a division tarnished by a political hiring scandal during President George W. Bush's administration and run for years by political appointees hostile to many of its long-term policies. He launched a record number of investigations into civil rights abuses and other misconduct at local police departments around the country. That includes a lawsuit last year accusing the office of law-and-order Arizona sheriff Joe Arpaio of racially profiling Latinos during a crackdown on illegal immigrants.

Perez also played a leading role in challenging laws in Texas and South Carolina that require voters to show photo identification to vote. A federal court later struck down the Texas law, saying it restricts minority voting rights, while another court delayed implementation of the law in South Carolina until after the 2012 election.

His nomination has broad support from labor and from the Latino community. Among those at the White House ceremony Monday were AFL-CIO President Richard Trumka and NAACP President and CEO Benjamin Jealous.

The nomination likely was delayed by the release last week of the Justice Department report. It found that Perez gave incomplete testimony to the U.S. Commission on Civil Rights when he said the department's political leadership was not involved in the decision to dismiss three of the four defendants in a lawsuit the Bush administration brought against the New Black Panther Party.

While the report concluded that Perez did not intentionally mislead the commission, it said he should have sought more information about the role of the agency's political leaders who participated in the decision to dismiss those charges.

Republican Sen. Charles Grassley of Iowa said Perez appeared to be "woefully unprepared to answer questions" from the Civil Rights Commission.

Other Republicans have cited his role in persuading the city of St. Paul, Minn., to withdraw a lending discrimination lawsuit from the Supreme Court. In exchange, the Justice Department declined to join two whistle-blower lawsuits against St. Paul that could have returned millions in damages to the federal government.

The St. Paul case had challenged the use of statistics to prove race discrimination under the 1968 Fair Housing Act, and Justice Department officials were concerned the court could strike down the practice.

Perez, once the top adviser to Sen. Edward Kennedy on civil rights, is a former career attorney at the Justice Department division he now leads.