President Obama on Monday nominated civil rights attorney Thomas Perez to be his next labor secretary, triggering what may be a heated confirmation battle with Republicans who dismissed the longtime Maryland progressive as too extreme on immigration and beholden to public employees unions.

Obama hailed the assistant U.S. attorney general for civil rights as a leader who "fought to open pathways into the workforce for everyone willing to contribute, including people with disabilities, LGBT Americans and immigrants."

But even before the White House announcement, the GOP was gearing up for a fight, one they said would make the recent confirmation hearing for Defense Secretary Chuck Hagel look mild by comparison.

Critics pointed to an audit released in recent days showing conflicts between liberal and conservative factions in Perez's division. The report, by a Justice Department inspector general, said Perez didn't address a rift between those who consistently promoted cases on behalf of minorities and those who thought the rights of white voters were being overlooked.

The investigator also questioned Perez's veracity in describing the department's decision to drop a voter intimidation case involving the New Black Panther Party. And some Republicans are calling for a congressional investigation into whether the Justice Department made a deal with the city of St. Paul, Minn., to withdraw from a Supreme Court housing discrimination case.

Perez served as Maryland Gov. Martin O'Malley's labor secretary -- the Democratic governor was in the front row for the announcement at the White House -- but for Washington-area residents, he's most known for his stint on the Montgomery County Council. Perez was on the council from 2002 to 2006 and represented the greater Silver Spring area.

His work in Maryland hasn't gone unnoticed by critics.

Sen. Jeff Sessions, R-Ala., hammered Perez for his time at Casa de Maryland, a Hispanic-rights advocacy group that Sessions said "instructed illegal immigrants on how to escape detection, and also promoted illegal labor sites and driver's licenses for illegal immigrants."

"This is an unfortunate and needlessly divisive nomination," Sessions added, calling Perez's views on immigration "far outside the mainstream."

And Sen. David Vitter, R-La., vowed to block the nomination, citing Perez's opposition to purging ineligible voters from the state rolls in the Southern state.

For weeks, labor unions have been trumpeting Perez's cause in anticipation of the announcement. And if confirmed, Perez would become the lone Hispanic in Obama's Cabinet, replacing Hilda Solis at the Labor Department.

Perez's nomination came after a report released by the Republican National Committee Monday, which suggested conservatives needed to pursue comprehensive immigration reform, among other measures to make the party more appealing to Hispanics.

The White House framed the GOP opposition to Perez as antithetical to that goal.

"The way the far right is reacting to the Perez [nomination] is likely to be included in the paperback version of the RNC report," quipped Obama senior adviser Dan Pfeiffer.

In nominating Perez, Obama made clear he would push a State of the Union proposal to raise the minimum wage to $9 an hour from $7.25 by the end of 2015.

"He understood that a minimum wage should be a wage that you can live on," Obama said, highlighting Perez's implementation in Maryland of the country's first statewide "living-wage law."