[...] President Barack Obama has threatened to veto the measure, and the Senate's vote indicates that supporters are far from the two-thirds majority that would be needed to override him. The Obama administration and its Democratic allies say the new rules are modest reforms that would simplify and streamline union elections and limit the ability of companies to drag the certification process out and gain time to fight a union's bid to win a certification election. The Senate vote took place under a rarely used law that limits debate on congressional attempts to reject agency rules, and bars opponents from stalling a final vote.