This article seeks to understand an understudied phenomenon: governmental players joining forces with non-governmental players in contentious actions against policies they want to prevent or redress. This behaviour, which we call ‘governmental activism’, problematizes important assumptions in the social movement literature on state–SMO dichotomies and on seeing ‘the state’ as a homogeneous and unified actor that solely provides the context for SMO activities. Governmental activism also problematizes assumptions on cooperation and ‘new’ modes of coordination in the governance literature. To understand governmental activism, we build on the strategic interaction perspective from social movement studies and on third-phase institutionalism from political science. In our analysis, we show the particulars of governmental activism. Our arguments are illustrated by empirical material on a case of municipal amalgamation in the Netherlands.