President Obama will formally nominate assistant U.S. Attorney General Thomas E. Perez as the next labor secretary on Monday, White House officials said, marking the first Latino selection to Obama’s second-term Cabinet.

Perez, 51, a first-generation Dominican American, is a former Montgomery County Council member who has overseen the civil rights division in the Justice Department since 2009. If confirmed, he would replace Hilda Solis, who resigned in January. The Washington Post reported last week that Perez’s nomination was expected, according to two sources familiar with Obama’s plans.

Administration officials described Perez as a “pragmatic leader and consensus builder” who oversaw the division that settled three major fair-lending cases and increased the enforcement of human trafficking laws.

Perez, who was Maryland’s state labor secretary under Gov. Martin O’Malley (D) from 2007 to 2009, has served in county, state and federal government.

But Perez's expected nomination, which must be confirmed by the Senate, has drawn criticism from Sen. Charles E. Grassley (R-Iowa). In a statement, Grassley said that if Perez is nominated, "he should face a lot of tough questions" about the Justice Department's role in a decision last year by St. Paul, Minn., to withdraw a housing discrimination case that was before the Supreme Court.

The Post reported that on civil rights, Perez's division oversaw voting rights cases against South Carolina and Texas. The Justice Department blocked a law in Texas last year that required voters to show a photo ID, following similar action in December 2011 in South Carolina. Both states filed lawsuits in U.S. District Court for the District of Columbia to overturn the federal action. The court struck down the Texas voter ID law and approved the South Carolina law, but ordered it delayed until at least this year.

The Civil Rights Division also conducted 17 investigations of police and sheriff's departments, the most in its 54-year history.

One of them involved the nation's self-proclaimed toughest sheriff, Joe Arpaio of Arizona's Maricopa County. The Justice Department sued him, his office and the county last year for civil rights violations after months of negotiations failed to yield an agreement to settle allegations that his department racially profiled Latinos in immigration patrols.

Perez’s nomination would help Obama respond to calls from the Latino community and other minority groups to add more diversity and women to his Cabinet. Hispanic voters overwhelmingly supported the president’s reelection bid last fall.

Perez could face questions during his nomination over a critical Inspector General report last week that found the department's voting rights section mired in deep ideological polarization and distrust, in some cases harming its ability to function over the past two administrations.

The 258-page review by Inspector General Michael E. Horowitz found "numerous and troubling examples of harassment and marginalization of employees and managers." The unprofessional behavior included racist and other inappropriate e-mails, Internet postings, blogs, and personal attacks by voting rights lawyers and staffers.

The Civil Rights Division oversees the voting section.

Several e-mails and Internet postings described in the report illustrated the contentious atmosphere in the voting section. In one, an employee characterized the neighborhood of a conservative career lawyer as a place where "everyone wears a white sheet, the darkies say 'yes'm' and equal rights for all are the real 'land of make believe.' " Another post by a career employee said that "a good, ethical Republican" is a "seeming oxymoron." One posting used the expression "po' Niggrahs" to describe a manager's attitude toward African Americans.

In a letter to the inspector general, Perez said he has tried to improve the professionalism of a section that, when he inherited it in the fall of 2009, had "low morale" and an "unacceptable degree of staff conflict." The report said the racist postings were made before Perez arrived.

"Since 2009, the Civil Rights Division and the Voting Section have undertaken a number of steps to improve the professionalism of our workplace and to ensure that we enforce the civil rights law in an independent, evenhanded fashion," Perez wrote in his response.

The investigation of the section started after Reps. Frank R. Wolf (R-Va.) and Lamar Smith (R-Tex.) sent letters to the inspector general questioning the department's handling of a case involving the New Black Panther Party. On Jan. 7, 2009, the Justice Department sued the group and several members for alleged voter intimidation. After the Obama administration came into office two weeks later, the department asked that the case against three of the four defendants be dismissed.

The inspector general's investigators reviewed more than 100,000 pages of documents and interviewed more than 135 people in scrutinizing the handling of that case.

A longtime resident of Takoma Park, Perez has a bachelor’s degree from Brown University, a master’s 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.

Sari Horwitz and Lena H. Sun contributed to this report.