In Allied Chemical & Alkali Workers of America, Local Union No. 1 v. Pittsburgh Plate Glass Co., 404 U.S. 157 (1971), the United States Supreme Court held that the collective-bargaining obligation extends only to the terms and conditions of employment and that the term "employees" does not include retirees under the National Labor Relations Act. The Court reasoned that "since retirees are not members of the bargaining unit, the bargaining agent is under no statutory duty to represent them in negotiations with the employer." Id. at 182 n.20, 399 n.20, 359 n.20. Despite this finding, however, the Court went on to state, "This does not mean that when a union bargains for retirees - which nothing in this opinion precludes if the employer agrees - the retirees are without protection. Under established contract principles, vested retirement rights may not be altered without the pensioner's consent. Id.