Republicans slammed President Obama’s selection of Thomas E. Perez as the next labor secretary Monday, painting the assistant U.S. attorney general as a polarizing and radical figure and suggesting that they will seek to hold up his nomination.

Perez, 51, a former Montgomery County Council member who has overseen the Civil Rights Division of the Justice Department since 2009, is expected to help Obama pursue an ambitious agenda that includes expanding voting rights, raising the minimum wage and overhauling immigration laws.

In announcing the selection in the East Room of the White House, Obama hailed Perez as a “consensus builder” whose story “reminds us of this country’s promise.” Perez, whose parents were from the Dominican Republic, would be the first Latino to join the second-term Cabinet if the Senate confirms him to replace Hilda Solis.

But several GOP lawmakers seized on a recent inspector general’s report critical of the Justice Department’s voting rights section to denounce Perez’s management style. They also pointed to the department’s role in persuading the city of St. Paul, Minn., to withdraw a housing discrimination case before the Supreme Court as evidence of his legal activism.

“Nominating somebody who is in the middle of a congressional investigation shows me that the president isn’t very serious about working together,” Sen Charles E. Grassley (R-Iowa) said in a statement.

Sen. David Vitter (R-La.) said he will block Perez’s nomination unless the Justice Department responds to a 2011 letter asking about the decision to sue his state for not providing voting-registration services to low-income residents.

“Perez was greatly involved in the DOJ’s partisan full court press to pressure Louisiana’s Secretary of State to only enforce one side of the law,” Vitter said in a statement.

The White House cited Perez’s work in settling three of the largest fair-lending cases and increasing enforcement of human-trafficking laws. While serving as the Maryland labor secretary from 2007 to 2009 under Gov. Martin O’Malley (D), Perez helped raise the minimum wage, and he has earned broad union support.

O’Malley, AFL-CIO President Richard Trumka, NAACP President Benjamin Jealous, and talk-show host and activist Al Sharpton were among the guests at the announcement.

In brief remarks accepting the nomination, Perez said he has learned “that true progress is possible if you keep an open mind, listen to all sides and focus on results.”

He also spoke briefly in Spanish, highlighting his Latino roots at a time when Obama is under pressure from minority groups to add more minorities and women to his Cabinet. Hispanic voters overwhelmingly supported the president’s reelection bid last fall.

A longtime resident of Takoma Park, Perez has a bachelor’s degree from Brown University, a master of public policy from Harvard and a doctorate from Harvard Law School. He and his wife, Ann Marie Staudenmaier, a lawyer with the Washington Legal Clinic for the Homeless, have three children.

Republicans raised red flags over a 258-page inspector general’s report last week that found the Justice Department’s voting section mired in ideological polarization and distrust, in some cases harming its ability to function over the past two administrations.

Inspector General Michael E. Horowitz found “numerous and troubling examples of harassment and marginalization of employees and managers.”

Perez has said the problems took place before his tenure at the Civil Rights Division, which oversees the voting section. The report found that he had given incomplete testimony during its investigation but that he did not intend to mislead investigators.

“This is an unfortunate and needlessly divisive nomination,” said Sen. Jeff Sessions (R-Ala.), a Judiciary Committee member.

William Branigin contributed to this report.

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