WASHINGTON —Sen. David Vitter quickly became the first senator Monday to pledge to block the nomination of President Barack Obama’s new choice to lead the Department of Labor.

Shortly after Obama nominated Thomas E. Perez as his new labor secretary, Vitter, R-La., announced that he would attempt to block the Senate confirmation until Vitter hears from the Department of Justice about a 2011 letter he sent to Attorney General Eric Holder concerning enforcement of the National Voter Registration Act.

Vitter alleged the Justice Department’s Civil Rights Division, which is headed by Perez, pressured Louisiana to enforce a part of the law to encourage the registration of more potential voters, such as welfare recipients, while not focusing as much on another part of the law to purge ineligible voters, such as the deceased, illegal immigrants and convicted felons.

At the time, the Justice Department had sued the state for not providing voter registration forms at some state government offices.

Vitter also expressed concern about Perez’s involvement in the dismissal of a voter intimidation case involving the New Black Panther Party in Philadelphia.

“Thomas Perez’s record should be met with great suspicion by my colleagues for his spotty work related to the New Black Panther case, but Louisianians most certainly should have cause for concern about this nomination,” Vitter said in his announcement. “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 — the side that specifically benefits the politics of the president and his administration at the expense of identity security of each and every Louisianian on the voter rolls.”

In his Nov. 15 letter to Holder, Vitter wrote that he was “deeply concerned” about the Justice Department’s alleged “selective enforcement” of the federal voter registration law.

“I am especially concerned that the Department appears to have refused to fulfill its duty for ideological and political reasons that have nothing to do with the impartial administration of justice,” Vitter wrote at the time.

In an email response, Sen. Mary Landrieu, D-La., said she would take time to assess the nomination and Perez’s record.

White House Press Secretary Jay Carney was quick to hit back at the concerns stated by Vitter and other Republicans. Carney defended Perez’s record and noted that Perez’s Civil Rights Division “has settled the three largest fair lending cases ever on behalf of families targeted by unfair mortgage lending practices.”

“The division has fought to protect the rights of every American student to achieve the quality education they will need to compete for the jobs of tomorrow,” Carney added. “It has dramatically increased the enforcement of human trafficking laws, and stepped up its efforts to ensure our nation’s veterans do not lose their civilian job because they are serving our nation.”

Earlier, Obama praised Perez, who would replace outgoing Labor Secretary Hilda Solis. Obama played up the background of Perez as the son of Dominican immigrants.

Perez worked as a garbage collector to help pay for college and became the first lawyer in his family, Obama said.

“Now, while he’s tackled plenty of tough issues, Tom has also spent a career as a consensus-builder,” Obama said. “He’s worked with CEOs; he’s worked with labor leaders. He’s worked at federal, state and local government levels.

“And, throughout, he understands that our economy works best when the middle class and those working to get into the middle class have the security they need on the job, a democratic voice in the workplace, everybody playing by the same set of rules.”