CHICAGO — Nontenure track faculty at the School of the Art Institute of Chicago are moving to organize with the Art Institute of Chicago Workers United, the union representing staff at both the Michigan Avenue museum and its school. At a rally on the Art Institute steps Tuesday afternoon, faculty called on their colleagues to join them in signing union authorization cards, the first step toward filing for union representation. “United we bargain,” they chanted. “Divided we beg.” In an open letter Tuesday announcing their intent to unionize, almost 200 adjunct professors and lecturers at the sc…