Pennsylvania Sen. Arlen Specter spent most of his political career being tagged as organized labor’s favorite Republican, a superlative that is now paying big dividends in the party-switcher’s Democratic primary against Rep. Joe Sestak.

When Specter defected from the GOP one year ago next month, he announced he would not be the “automatic 60th vote” on the Employee Free Choice Act — the top legislative priority for unions.

But with 10 weeks to go until the May 18 primary, Specter doesn’t appear to have lost any ground with his friends in the Keystone State labor community, even though Sestak boasts he was an original co-sponsor of the EFCA legislation.

“The Senator was in some respects held to a higher standard among labor after April 28,” said state Democratic Party Chairman T.J. Rooney, a Specter supporter. “It’s one thing to be a Republican who votes with you when it counts, it’s another thing to be a Democrat.”

Truth be told, the fact that most unions are sticking by Specter isn’t too surprising given that many labor groups, including the statewide AFL-CIO, supported Specter in his 2004 re-election race. But wooing union support in a Democratic primary is a whole different ballgame.

“Yeah, it was easier,” Specter said in a phone interview last week. “They said, ‘We’ve supported you when you were a Republican, and that was a bridge we had to hurdle. And now that you’re a Democrat, it’s easier.'”

There are several major labor endorsements still to come in the primary, including the state AFL-CIO, which will meet next month to endorse a candidate. Pennsylvania AFL-CIO President Bill George said, however, that Specter appears to already have the two-thirds support necessary from the organization for an endorsement.

George added that the original EFCA bill is in the past, and Specter has won union support by working with his colleagues to create a compromise on the legislation, which national labor organizations are hoping will get a vote after health care reform is passed.

“It’s like water over the damn,” George said. “That first bill’s gone and consequently, it’s time to move forward. And Arlen Specter was very instrumental with other Senators getting an agreement.”

Specter has already announced endorsements from other labor groups, both inside and outside the AFL-CIO, which, according to his campaign, translates to support from more than 380,000 union members. A campaign aide for Sestak, meanwhile, said he has been endorsed by the United Food and Commercial Workers International Union and a couple local chapters of the United Steel Workers and the bricklayers and postal unions.

Sestak said that while Specter may have the lion’s share of labor endorsements, he remains confident that when voters go to the polls the cracks in that support will be evident.

“While I respect organized labor’s leadership, it frankly has to do with working families,” Sestak said. “I know that Arlen Specter has made some deals with the labor leaders, but the rank and file” will support me on Election Day.

There are several theories as to why Sestak’s upstart campaign has never gotten off the ground.

Public polls have consistently shown Specter with a lead over Sestak, including a Research 2000 poll taken March 8-10 that had Specter ahead 51 percent to 32 percent.

That’s not a big difference from a similar poll from late August that showed Specter with a similar 48 percent to 33 percent lead over Sestak. Both polls were paid for by the liberal Web site Daily Kos.

And in addition to Sestak not yet overcoming a name identification hurdle, some high-ranking Pennsylvania Democrats described the Congressman’s frenetic personality as one of the reasons he has not yet waged an effective campaign against Specter.

“He doesn’t have a campaign manager,” said one Democrat. “That’s the beginning, middle [and] end of the problem. He’s raised $5 million or $6 million, and he doesn’t have a campaign manager.”

Sestak, however, said his campaign is just beginning to launch. He reported having $5 million in the bank at the end of 2009, and he said he has plans to “without a question” spend every penny of it leading up to the primary if necessary. Specter reported having $8.7 million in the bank as of Dec. 31.

In fact, Specter has even succeeded in making Sestak’s campaign payroll a labor-related issue in the campaign. Specter and his allies have alleged that the vast majority of Sestak’s staffers earn under the minimum wage based on the long hours they work and low pay they receive — and therefore charge that he is in violation of the labor laws he supports.

“Congressman Sestak has a lot of money,” Specter said. “He has over $5 million in the bank and he’s kept it because he’s paying his employees less than the minimum wage.”

It’s an allegation that Sestak described as “silly.”

“How silly,” Sestak said. “Here we are fighting two wars overseas, one more war at home, health care system that’s broken … and he wants to focus on my wonderful staff, who has come here to do hard work and volunteer,” Sestak said.