With Democratic Senators continuing to work out a possible “card check— compromise, organized labor is getting antsy about the exact terms of the deal and worrying that its legislative window may be closing.

“Right now, the entire movement is together,— a union lobbyist said. “But then again, we don’t have a piece of paper that says, This is what we’re going to do.’—

Union sources said they’re hoping preliminary changes to the Employee Free Choice Act will emerge by the weeklong July Fourth recess, giving lawmakers enough time to vote on the bill by August.

The bill, which would make it easier for workers to unionize, is the source of closed-door negotiations led by Sen. Tom Harkin (D-Iowa), who has said he wants a vote next month.

Harkin continued to meet last week with Democratic Sens. Charles Schumer (N.Y.), Mark Pryor (Ark.) and Arlen Specter (Pa.) on an EFCA rewrite. The quartet is working out a deal in the hopes of picking off a handful of votes to reach the 60 needed to cut off debate in the chamber.

American Rights at Work, the labor-backed coalition pushing card check, is tentatively supporting a prospective deal, so long as it maintains EFCA’s three key planks: a majority sign-up for union elections, increased penalties for employers for labor violations and mandatory arbitration.

The coalition — as well as other unions — said it’s staying mum on the specifics of any future bill until a new compromise emerges from the ongoing Senate talks.

“We are making it abundantly clear that whatever piece of legislation comes out, that it remains true to the three fundamental principles that EFCA was built upon: a fair and direct path to form a union, real penalties for employers that violate the law, and solutions to help workers and employers reach a first contract in a reasonable period of time,— American Rights at Work spokesman Josh Goldstein said. “Any piece of labor law legislation will be judged on those fundamental principles.—

Service Employees International Union Secretary-Treasurer Anna Berger, through a spokesperson, hinted that her union might be willing to deal, saying SEIU was committed to the principles of card check but not necessarily wedded to EFCA’s exact wording.

“We are firmly committed to principles behind the Employee Free Choice Act,— Berger said. “We are strongly in favor of a bill that includes all three components.—

Labor’s wait-and-see approach differs drastically from the rigid tactics of the U.S. Chamber of Commerce and the Committee for a Level Playing Field, two business-backed groups that are pledging no compromise on card check.

A strategist involved in card check talks said both sides “are engaging in wishful thinking— on their opposition’s chances: Business groups doubt lawmakers will spend the political capital on card check with other important legislation in the hopper, while labor groups — coming off huge electoral victories last November — are unwilling to accept the political reality.

“Both of them are engaged in the same mistaken assumption: One thinks they can’t get to 60, the other thinks they can get to 60,— the source said.

While lawmakers continue to work out the details, a union lobbyist said AFL-CIO Legislative Director Bill Samuel remains the point person between the Hill and organized labor, holding a weekly meeting with union leaders that lays out the myriad EFCA proposals being floated, including a vote-by-mail option for union elections and “last best— arbitration that is used in Major League Baseball to settle salary disputes.

Samuel did not respond to messages left at his office seeking comment.

If and when a deal emerges, another union lobbyist predicted that not everyone will be pleased, possibly jeopardizing its chances.

The lobbyist warned that Senate Majority Leader Harry Reid (D-Nev.) and his aides could decide that EFCA was not worth the political risk if, in addition to fighting off the U.S. Chamber of Commerce, they have to deal with union infighting.

“There’s going to be somebody unhappy with it,— the lobbyist said of an eventual compromise. But “if [the unions] don’t stick together, then Harry Reid is not going to have his people walk the plank.—

And should Reid decide to abandon card check this cycle, the lobbyist predicted that EFCA likely is dead until at least 2011.

“The unions have a lot to lose and a lot to gain,— the source said. “They’ve got to be smart about this and understand that if you wait too long, it’ll never happen.—