Union officials will launch a major grass-roots drive for “card check— legislation during the two-week spring break, targeting possible GOP Senate pickups and potentially wavering Democrats in an all-out push for the labor organizing bill.

The new effort, being organized by officials from the AFL-CIO, Change to Win and the American Federation of State, County and Municipal Employees, signals that labor has not given up on passing the current version of the Employee Free Choice Act, which appears two votes short of the 60 needed to move it.

The legislation would make it easier for workers to unionize by giving them the right to union recognition after a majority of workers have signed pro-union cards.

Labor officials expect one more pro-card check vote if Al Franken (D) is seated as a Minnesota Senator, a prospect that they believe became much more likely after a judicial ruling Tuesday against former Sen. Norm Coleman’s (R) quest to count more absentee ballots.

The other vote will have to come from the Republican camp. Democrats are expected to back the unions on procedural votes requiring 60 Senators, but union officials feel they need to stiffen a couple of spines nonetheless.

With the decision of Sen. Arlen Specter (R-Pa.) to oppose the measure, union officials know the road ahead is difficult. But they are not ready to compromise, as some expect to happen.

“We’re going at this full throttle,— said a labor official with knowledge of the grass-roots campaign.

Some 20 field staff have already been tapped to begin operations in an undisclosed number of states. Among those in the crosshairs are Specter and Maine Republican Sens. Susan Collins and Olympia Snowe.

The effort will feature a huge leafleting drive at workplaces, accompanied by phone calls and letters to lawmakers.