Our research builds on existing literature examining institutional voids in emerging economies. Using data from two cases of mining FDI in Argentina, we conceptualize the triggers, processes and consequences of informal institution-building by a social movement. We found the cases to exhibit different ‘community sustainability orientations’, enabling two contrasting strategies, ‘bargaining’ and ‘gatekeeping’, to address the existing institutional void. This led to the development of new formal institutions – regulated CSR for the former and legal ban on mining operations for the latter case. Our study thus offers insights into the processes through which institutional entrepreneurship by social movements influences MNEs.