In 1918, seven years later, the Court unanimously reaffirmed the rule of reason in "Chicago Board of Trade v. United States". In an opinion written by Justice Louis Brandeis, the Court held that an agreement between rivals limiting rivalry on price after an exchange was closed was reasonable and thus did not violate the Sherman Act. The Court rejected a strict interpretation of the Sherman Act's language: "The true test of legality is whether the restraint imposed is such as merely regulates and perhaps thereby promotes competition or whether it is such as may suppress or even destroy competition." The Court did so mostly because the agreement was regulatory rather than anticompetitive.