WASHINGTON -- The head of the nation's largest federation of unions on Monday blasted congressional Republicans of pushing a "sleazy legislation" that exploits an unfair labor practice dispute over Boeing's new jetliner-assembly plant in South Carolina, a bill he says panders to the "radical ideology" of the tea party while selling out workers' rights.

Richard Trumka, president of AFL-CIO, said the legislation introduced by House Republicans would render the National Labor Relations Board (NLRB) toothless in taking action against employers who commit unfair labor practices. That, Trumka told reporters during a conference call, would roll back decades' of protection for workers while rewarding "a major corporate donor, Boeing."

Trumka's denouncement was the latest volley in a case that has become a major political cause for conservatives. The NLRB in April filed a complaint against Boeingfor allegedly deciding to build its first-ever final-assembly plant outside of Washington state as a retaliation and a warning to its Machinists. The union's members have gone on strike five times against the company since 1977.

The NLRB contends the move was illegal and is seeking to force Boeing to bring back the work to Everett, regardless of whether the South Carolina plant remains open. An NLRB administrative law judge in Seattle has been hearing the case since June, and it's unclear when he might issue a final ruling.

Rep. Darrell Issa of California, chairman of the Committee on Oversight and Government Reform, has accused Lafe Solomon, the NLRB's action general counsel who filed the complaint, of overstepping his authority.

Julius Getman, a University of Texas law professor who joined Trumka's call, said the Republicans' bill has sparked "considerable outrage" among academics and labor-law experts. The bill would strip the NLRB of its current remedies for illegal employer conduct. The board could not, for instance, order a company to reinstate work, cancel outsourcing or relocation or require investment in a plant that lost work to alleged retaliation.

The legislation is "an attack on basic rights of workers," Getman said.

The NLRB is an independent federal agency charged with ensuring fair labor practices. It protects workers' right to form and join unions and to wage strikes. It also enforces rules barring unions from engaging in picket-line misconduct or retaliating against non-strikers. Last week, the agency sought and received a preliminary injunction against two longshoremen's unions over a violence-marred picketing at a grain-processing plant in Longview.