Speaking at a labor rally this weekend, Pennsylvania Sen. Arlen Specter voiced support for the Employee Free Choice Act, a turn of events that could revive the hopes of a bill many felt was doomed.

The legislation, which is sponsored by Iowa Sen. Tom Harkin, makes it easier for labor unions to organize. Iowa Republican Sen. Charles Grassley said his party would filibuster the bill, which led Harkin to predict it would have to be altered to have any chance of passing.

Specter, who once supported the measure (and even sponsored it), came out in opposition to it in March. Most believe the about-face was due to a strong challenge in the Republican primary. Since that time, however, Specter has become a Democrat. U.S. Rep. Joe Sestak, a retired Navy Admiral, has publicly expressed an interest in challenging him in the 2010 Democratic primary, pressuring Specter from the left.

Specter’s speech this weekend in Pittsburgh appears to signal another change in opinion that could give the Democrats the votes needed to overcome a filibuster and make Harkin’s bill a reality.

“If you want to be elected in this state, you have to come to labor,” he said. “I know that. I owe my re-election in part to the endorsement the AFL-CIO has given me in the past.”

Specter was then interrupted by a man in the crowd who declared “you want my vote, I want yours,” referencing Specter’s position on the bill.

“I understand your job’s on the line,” Specter said. “I think you’ll be satisfied with my vote on this issue.”

The contentious portion of the bill involves language that would allow unions to be certified by the National Labor Relations Board if a majority of workers sign cards designating the union as their bargaining representative. It would not do away with secret ballots for union organizing, but they would no longer be required. Union activists and anti-labor groups both agree that the change would make it easier for unions organize.

Opponents say that without a secret ballot, workers will be intimidated into joining a union. Supporters of the bill counter that employees already face intimidation from their employer when contemplating a union vote. Under the current law employers can veto workers’ decision to organize through majority signup and force them into the election process where, according to a recent study, a pro-union worker is illegally fired in a quarter of all organizing drives.