Previous research has emphasized corporate lobbying as a pathway through which businesses influence government policy. This article examines a less-studied mode of influence: private regulation, defined as voluntary efforts by firms to restrain their own behavior. We argue that firms can use modest private regulations as a political strategy to preempt more stringent public regulations. To test this hypothesis, we administered experiments to three groups that demand environmental regulations: voters, activists, and government officials. Our experiments revealed how each group responded to voluntary environmental programs (VEPs) by firms. Relatively modest VEPs dissuaded all three groups from seeking more draconian government regulations, a finding with important implications for social welfare. We observed these effects most strongly when all companies within an industry joined the voluntary effort. Our study documents an understudied source of corporate power, while also exposing the limits of private regulation as a strategy for influencing government policy.