This directly from the NLRB today:
The National Labor Relations Board has determined not to seek en banc rehearing in Noel Canning v. NLRB, in which the U.S. Court of Appeals for the DC Circuit held that the January 4, 2012 recess appointments of three members to the Board were invalid. The Board, in consultation with the Department of Justice, intends to file a petition for certiorari with the United States Supreme Court for review of that decision. The petition for certiorari is due on April 25, 2013.
Rather than ask the U.S. Court of Appeals for the DC Circuit to rehear the case with a full bench, the board will instead ask the Supreme Court to review the ruling.