WASHINGTON — Republicans say they aren't prepared to celebrate after the National Labor Relations Board dropped its high-profile lawsuit against Boeing on Friday. The Machinists union approved a four-year contract extension with Boeing this week, in which it agreed to withdraw allegations that the company built a nonunion plant in South Carolina to retaliate against past union strikes in Washington state. In return, Boeing promised to build the new version of its 737 airplane in Washington state. GOP Sen. Lindsey Graham of South Carolina says the case should never have happened and is calling on Congress to investigate whether the union and board collaborated against Boeing. Republican presidential contender Mitt Romney, meanwhile, called the NLRB a "rogue agency that tramples on the rights of American workers and businesses." Boeing spokesman Tim Neale said the company continues to believe the complaint was without merit and should have been dropped.