ABC News’ Rick Klein reports: A second prominent labor leader told ABC News today that Sen. Arlen Specter is not guaranteed to get union support in next year’s Democratic primary, as Specter’s position on the Employee Free Choice Act draws continued scrutiny. Andy Stern, the president of the SEIU, today met with Rep. Joe Sestak, D-Pa., who is considering running against Specter. Specter, D-Pa., left the Republican Party last week and announced that he’d run in the Democratic primary in 2010. After the meeting, Stern said he told Sestak that, based on conversations with labor leaders in Pennsylvania, Specter is highly unlikely to get the support of organized labor if he votes against EFCA, the pro-unionizing measure that critics call "card-check." "There’s no way they’re ever going to be supporting someone who is seen as thwarting this opportunity," Stern told ABC. "It is hard to imagine any union supporting a candidate in the Democratic Party for the US Senate who doesn’t have strong positions on both healthcare and Employee Free Choice." Stern stressed that he is not endorsing any candidate. Though Specter has maintained his opposition to EFCA — a position he reiterated yesterday on the Sunday talk shows — Stern said he hopes Specter will ultimately support a compromise. "No one’s going to get exactly what they want," he said. "So the question is, where is his flexibility, on not letting his idea of perfection stand in the way of progress." Labor leaders in Pennsylvania, Stern said, "will evaluate where he stands not just based on what he says, but what he does." Sestak supports the Employee Free Choice Act, which would make it far easier for workers to form unions, but which is fiercely opposed by business interests that are casting the bill as a job-killer. Today on ABCNews.com’s "Top Line," Richard Trumka, the secretary-treasurer of the AFL-CIO, also warned that Specter may not get labor support, despite the commitment of Democrats led by President Obama and Gov. Ed Rendell, D-Pa., to support Specter next year. Said Trumka: "Those decisions will be made by people in the state, and our members in the state know who will stand with them. And if Arlen Specter — he stood with them in the past — if he continues to stand with them, they’ll support him. If he doesn’t, they won’t support him." Sestak told Greg Sargent of The Washington Post’s Plum Line blog today that he’s likely to get in the race if Specter doesn’t change some of his positions. "If he doesn’t demonstrate that he has shifted his position on a number of issues, I would not hesitate at all to get in," Sestak said.