* Former union lawyer will be labor board's top prosecutor
* U.S. Supreme Court set to settle related battle (Updates with Senate confirming Griffin)
A divided U.S. Senate on Tuesday confirmed a former union lawyer picked by President Barack Obama to be the top prosecutor at the National Labor Relations Board.
With Obama's Democrats rejecting Republican fears that Richard Griffin would bring an unfair labor bias to the board, the Senate approved him as the NLRB's general counsel on a mostly party-line vote of 55-44.
The board, which oversees union elections and polices unfair labor practices, has long been a point of friction between pro-union Democrats and pro-business Republicans.
While the battle over Griffin ended, a wider struggle over the NLRB and the power of the presidency remained to be played out before the U.S. Supreme Court.
Until a court ruling in January against the White House, Griffin served for a year on the NLRB as a contested Obama appointee. Before that, he was general counsel for the International Union of Operating Engineers.
Obama nominated him in August to be NLRB general counsel.
The five-member board of the NLRB makes its ultimate case determinations, but the general counsel plays a critical role as a gatekeeper, investigating alleged labor violations and deciding which cases should be prosecuted.
Before the vote on Tuesday, Republican Senator Lamar Alexander of Tennessee declared his opposition to Griffin, saying: "I'm concerned about the direction of the NLRB as an advocate more than an umpire.
"I do not believe his presence as general counsel will improve the situation."
Democratic Senator Tom Harkin of Iowa, chairman of the Senate Labor Committee, which approved the Griffin nomination, hailed the nominee and his knowledge of labor laws.
"Mr. Griffin is exceptionally well qualified," Harkin said. "I have no doubt he will do an outstanding job of enforcing our nation's labor laws for workers, unions and employers."
Harkin pointedly noted that years ago, an NLRB member came to the board directly from the U.S. Chamber of Commerce, the nation's biggest business group, without any complaints of bias from Republicans.
"I guess it is only when you represent labor unions that you are biased, not when you represent the Chamber of Commerce," he said.
In January 2012, when the Senate was technically in session but not conducting business, Obama appointed Griffin and Sharon Block as NLRB board members.
Objections from Republicans led to a deal later in which Obama withdrew the nominations of Griffin and Block, opening the way for Senate confirmation of other board members seen by Republicans as more moderate.
Those confirmations gave the NLRB its first full slate of board members in a decade. The board's actions in the interim, however, have fallen under a cloud of legal uncertainty.
The Supreme Court agreed in June to hear the case of NLRB v. Noel Canning at the request of the administration. The court is expected to hear oral arguments sometime during its current term, which began this month and will run to June.
The administration went to the high court after a federal appeals court in Washington, D.C., ruled in January that the NLRB did not have a quorum when it ruled against Noel Canning, a bottling company, because three of the five sitting members were not valid appointments. The board needs three members to have a quorum. The ruling cast into doubt hundreds of NLRB decisions.
Obama's so-called "recess appointments" of the three members that were judged invalid took place on Jan. 4, 2012.
Presidents from both parties have used recess appointment authority over the years when facing difficulties winning Senate approval of nominees. The appeals court ruling severely curtailed the scope of the recess appointment power.
Noel Canning, backed by the U.S. Chamber of Commerce, had argued that an NLRB ruling for the International Brotherhood of Teamsters in a disagreement over failed contract negotiations, could not be enforced due to the recess appointment issue.
Other appeals courts, including one in Richmond, Virginia, in July, have issued similar rulings finding the recess appointments invalid.