Now that Republicans have picked up their 41st seat in the Senate, breaking up the Democrats' 60-vote supermajority, President Obama's legislative agenda is up in the air, including his nominees for federal agencies.

The latest example is union lawyer Craig Becker, whose nomination for the National Labor Relations Board was narrowly approved by a Senate panel on Thursday but who may not be taking the post anytime soon.

GOP lawmakers, including Arizona Sen. John McCain, have vowed to place a hold on his nomination, claiming that Becker would make pro-union changes on the NLRB without congressional approval.

Thursday's 13-10 party line vote in the Senate Health, Education, Labor and Pensions Committee sends Becker's nomination to the Senate floor, but the loss of a Democratic seat in the Senate makes his fate uncertain. With Republican Scott Brown sworn in Thursday as senator from Massachusetts, Democrats no longer have the 60 votes needed to overcome a filibuster if the GOP lines up to block the nomination.

A key procedural vote is scheduled for Monday.

Republican Sens. Mike Enzi of Wyoming and Lisa Murkowski of Alaska previously supported Craig's nomination when the committee voted on his nomination in October. But the two reversed their decision on Thursday, voting against Becker, who had to be re-nominated by President Obama this year after a barrage of business groups lobbied against him.

Becker, who currently serves as associate general counsel to the Service Employees International Union (SEIU), a labor union representing about 1.8 million workers, was approved in October by the Senate Health, Education, Labor and Pensions Committee.

But McCain and a slew of business groups have raised questions over articles and academic journals written by Becker on the very labor law he would work to interpret if confirmed to the board. Critics say Becker's writings reflect views that support restricting employers' free speech rights and limiting the ability of employers to converse with their employees during union representation campaigns.

Of particular concern to critics is a 1993 Minnesota Law Review article in which Becker, then a law professor at UCLA, argued that "employers should be stripped of any legally cognizable interest in their employees' election of representatives."

"Employers should have no right to raise questions concerning voter eligibility or campaign conduct," Becker wrote.

"Because employers have no right to vote, they cast no ballots the significance of which can be diluted by the inclusion of ineligible employees. Nor, obviously, can employers be coerced in the exercise of a franchise they do not have. Because employers lack the formal status either of candidates vying to represent employees or of voters, they should not be entitled to charge that unions disobeyed the rules governing voter eligibility or campaign conduct," he continued.

Republicans continued to express concerns after a Tuesday confirmation hearing for Becker, claiming many of the nominee's answers were ambiguous.

In his opening statement at Tuesday's hearing, Becker pledged to "remain faithful to the will of Congress" and "apply the law impartially and fairly."

"I've learned to appreciate the concerns of employers and often have been able to find common ground between labor and management," he said. "I've represented both sides in unfair labor practice cases."

The Democrats have stood strongly behind his confirmation.

HELP Committee chairman Sen. Tom Harkin, D-Iowa, on Tuesday called Becker an "obviously well-qualified nominee," who "brings a tremendous depth of experience to this position."

"There's no question that Mr. Becker has been thoroughly vetted for this position," Harkin said, as he acknowledged criticism from some over Becker's past academic writing.

"He has taken a critical approach to existing law -- nothing wrong with that. That's what academics are supposed to do, to contribute to the marketplace of ideas."

Brown, Massachusetts' new senator, refuted claims Thursday that he was rushed to Washington at the request of Republican colleagues to block Becker's confirmation.

"I've had no contact with the leader's office," Brown told reporters.  "I'm an independent voter and thinker -- I always have been." 

Fox News' Trish Turner contributed to this report.