"That exemption stems from the Supreme Court’s interpretation of the Anti-Racketeer­ing Act of 1943, known as the Hobbs Act. That law forbids the obstruction of interstate commerce by robbery or extortion. It’s the main federal law against extortion (economic gain through violence). Unions’ exemp­tion is rooted in the 1973 Enmons case, in which the Supreme Court ruled that unions are exempt because the law simply doesn’t apply when unions are seeking “legitimate” union objectives. The case involved three members of the International Brotherhood of Electrical Workers (IBEW) who were indicted for firing high-powered rifles at three utility company transformers. The oil that drained from one of the transformers blew up a substation. The U.S. District Court in Baton Rouge, Louisiana, dismissed the charges against the IBEW, arguing that the actions were not illegal since they were done to obtain legitimate union objectives. Writing for the 5-4 majority, Justice Potter Stewart put the onus back on Congress for creating a loophole in the Hobbs Act.[...] Thousands of violent acts have gone unpun­ished as a result of Enmons. For example, the National Institute for Labor Relations Research identified 8,799 incidents of union-related violence between 1975 and 1998. Less than 3% of these incidents resulted in convictions, according to the Institute."