NEW YORK—A federal labor board postponed a scheduled vote count that was to have taken place on Wednesday that would determine whether three more Starbucks Corp. locations in Buffalo, New York, will join a union. Because the National Labor Relations Board (NLRB) had not ruled on an outstanding appeal by Starbucks’ by the time votes were to be tallied, the board impounded the ballots to be counted in the future. Even so, momentum to unionize more of the company’s locations in the United States continues to build. In just the last six months, employees at more than 100 stores in at least 26 states have petitioned the NLRB to hold union elections in their locations–including flagship Reserve Roastery locations in New York and Seattle, Starbucks’ hometown. The union is also winning its legal arguments. On Wednesday, the NLRB rejected an appeal by Starbucks to alter election procedures for a cafe …