CHARLESTON, S.C. (AP) — The machinists union on Monday asked for an election so about 2,500 Boeing production workers in South Carolina can decide whether they want union representation. Under National Labor Relations Board rules, 30 percent of the workers in a potential union bargaining unit must sign authorization cards for an election to be held, said Frank Larkin, spokesman for the International Association of Machinists & Aerospace Workers. Boeing has this ugly practice of pitting state against state and worker against worker, and a collective bargaining agreement can help level that playing field for workers. Four years ago, shortly before the company opened its $750 million Dreamliner plant, the NLRB filed a complaint against Boeing alleging that the nonunion plant in South Carolina was in retaliation against union workers in Washington state who held a strike in 2008.