United States Steel Corp. said Wednesday that an arbitration board has ruled in favor of Nippon Steel Corp.’s plan to acquire the Pittsburgh company, a deal opposed by its union. The nonbinding decision was made by the Board of Arbitration whose members were selected by U.S. Steel and the United Steelworkers, a powerful union that called in January for scrutiny of the acquisition deal, citing financial and other concerns. David Burritt, CEO of the company, said, “With the arbitration process now behind us, we look forward to moving ahead with our pending transaction with Nippon Steel.” The lab…