A US labour board dismissed a politically charged lawsuit on Friday that accused Boeing Co of illegally punishing union workers for past strikes by opening a non-union assembly plant in South Carolina. The National Labour Relations Board decision, affirmed by the administrative judge hearing the case in Seattle, was made possible by a contract settlement between the aerospace giant and the International Association of Machinists that ensured union workers would assemble its newest 737 jetliner. Boeing shares ended 2.5 per cent higher at $71.93 on Friday as investors applauded labour certainty at a company with a large order backlog. The NLRB disposed of a case that had energised Republicans and was a political headache for the Obama administration.