Survey research shows that foreign-born Latinos in the USA are among the least likely to participate in political activism. Yet during the spring of 2006, up to five million (mostly Latino) immigrants and their allies took part in a historic national protest wave. This article examines how nativist legislation can spark immigrant large-scale collective action in an unexpected location. The case of Fort Myers, FL illustrates the cognitive mechanisms that help explain why and how external threats can transform a latent sense of group membership among unconventional protest organizers (e.g. immigrant soccer league members and ethnic small business owners) into a willingness to take action and utilize pre-existing community resources for the purpose of mass mobilization. These findings have important implications for Latino politics, immigration, and social movement scholars.