SAM HANANELWASHINGTON (AP) ¿ In a setback for organized labor, Pennsylvania Sen. Arlen Specter said Tuesday he will oppose a bill that would make it easier for workers to form unions. Specter was the only Republican to support the Employee Free Choice Act two years ago, and unions were hoping he might be the crucial 60th vote needed to overcome an expected GOP filibuster of the measure when it's taken up this summer. Specter has faced unusually heavy pressure from both labor and business interests and is likely to face a tough Republican primary challenge next year from former Pennsylvania Rep. Pat Toomey. In a statement, Toomey called Specter's decision a "flip flop," prompted by the threat of primary opposition to the five-term senator. In a floor speech, Specter called the organizing bill a "very emotional issue with labor looking to this legislation to reverse the steep decline in union membership and business expressing great concern about added costs, which would drive many companies out of business or overseas." Business groups, who have already spent more than $20 million to lobby against the bill, applauded the decision.