Abstract Policies constraining nonprofit and civil society activity have been documented in multiple countries. A less widespread phenomenon, but one that is also worth exploring, is the enactment of laws intended to promote civil society. What happens when laws are enacted to promote these organizations? How effective are these laws? Building on insights from the literature on nonprofit formation and organizational ecology, this paper adopts a quasi-experimental approach, to analyze the effect of passing a state-level law of Civil Society (CSO) sector promotion on the number of newly-constituted CSO organizations. Using data from Mexico, between 1990 and 2018, the paper uses the synthetic control method to examine this effect, separately, in 3 Mexican states, against a pool of 13 states which had not enacted a law of this kind during the period under study. The results show quite different effects across states, and point to the need of exploring in depth the policy process surrounding the passing of the law. These mixed patterns also call for further examination of the broader context where CSO laws take effect, and the incentives and disincentives local actors may perceive in the content of the laws.