President Obama faces a potentially big Senate battle over his nominee for Labor secretary, Thomas Perez.

Senate Minority Leader Mitch McConnell, R-Ky., served notice of Republican opposition by saying that Perez has abused his authority as head of the civil rights division of the Justice Department.

Calling Perez "a crusading ideologue," McConnell said he "seems to view himself as free to employ whatever means at his disposal, legal or otherwise, to achieve his ideological goals."

The Republicans used a procedural move Wednesday to delay a vote on Perez before the Senate Health, Education, Labor and Pensions Committee. It has been pushed back to May 16.

White House officials and congressional Democrats denounced GOP opposition to Perez as pure politics.

"The bottom line is that Tom Perez is a dedicated public servant who has spent his career fighting to keep the American Dream within reach for hardworking, middle-class families and those striving to get into the middle class," said White House spokesman Jay Carney.

The question is whether Republicans will seek to bottle up the Perez nomination.

It is possible that at least one Republican senator will seek a filibuster of Perez, requiring the Democrats to round up 60 votes to move the nomination through. The Senate Democratic caucus has 55 members.