Primary care physicians at Mass General Brigham voted overwhelmingly in favor of forming a union on Friday amid a dispute with the hospital system over their bargaining unit's size. Of the 237 eligible physicians, 209 participated in the mail-in election earlier this month, with 88% of voters in favor of unionization. If certified, the union — representing all full-time, part-time, and per diem primary care physicians at Mass General Hospital and Brigham and Women's Hospital — will join the Doctors Council, an affiliate of the SEIU. But the union will be unable to begin negotiating a contract until it resolves a legal battle with the hospital system over the size of its bargaining unit.