R.I. Gen. Laws § 39-17-6: Rate increases during term of franchise.

No corporation which shall acquire exclusive rights or franchises under the provisions of this chapter, shall at any time during the continuance thereof charge for its product, wares, or service, to any town or city or the inhabitants thereof, any greater price than the price actually charged by it at the time of the granting of the rights or franchises, both prices being reckoned in United States gold coin of the standard weight and fineness in force at the time of the granting of the right or franchise, or in the equivalent thereof in actual value in other lawful money of the United States.