A U.S. Senate panel today split largely along partisan lines today to send President Barack Obama’s two nominees to the National Labor Relations Board to the Senate floor.

Sen. Lamar Alexander, R-Tenn., the top Republican on the Democratic-led Senate Health, Education, Labor and Pensions Committee, voted against confirming Nancy Schiffer, a former AFL-CIO associate general counsel, and Kent Hirozawa, the NLRB’s Democratic chairman’s chief legal counsel.

“My primary concern is the ability of the two to set aside their pro-union advocacy past and act as neutral arbiters between employees and employers, so those parties can trust them to fairly adjudicate labor disputes,” Alexander said. “Will they be judges and not advocates? So far, my concerns haven’t been lessened.

The confirmation vote was 13-9. Republicans have complained the five-member board hasn’t been impartial enough in dealing with disputes between employers and unions.