Adjuncts at Boston University voted by a two to one margin to form a union affiliated with Service Employees International Union, they announced Wednesday. Some 750 adjuncts make up the union, which is part of SEIU's Faculty Forward campaign to organize part-time professors around Boston. Adjuncts already have formed unions at Tufts, Lesley and Northeastern Universities. Laurie LaPorte, an lecturer in anthropology at Boston University, said in a statement that organizing "started with a simple premise: if excellence in learning is the core mission of our university, then we need real investment in the classroom -- in the equitable, sustainable treatment of all educators." Colin Riley, university spokesman, said that the institution is "looking forward to working with the union representing our adjunct faculty."