Four former Teamsters Union leaders who handled labor activities at Boston’s two convention centers were accused Wednesday of effectively shaking down businesses across the city while physically threatening and harming rank-and-file union members in order to maintain their control over the union. The four former Teamster Local 82 leaders — John Perry, 60, of Woburn; Joseph “Jo Jo” Burhoe, 44, of Braintree; James “Jimmy the Bull” Deamicis, 49, of Quincy; and Thomas Flaherty, 49, of Braintree — were charged in a 30-count federal indictment with racketeering, conspiracy to extort, extortion, attempted extortion, mail fraud, prohibition against certain persons holding office, and theft of government money, according to US Attorney Carmen M. Ortiz’s office.