In this paper, we use social movement theory to better understand the recent wave of employee activism in the high-tech sector. Through a comparative case examination of four recent examples at Microsoft, Google, Wayfair, and Amazon, our analysis focuses on three important aspects of employee activism – opportunity structures, tactics and mobilization, and outcomes. We find that activists who exploited multiple opportunity structures were more effective and that when managers provided a positive yet unsatisfactory response to initial activist demands, activists shifted from persuasive to more confrontational tactics. In addition, although none of these examples can be categorized as comprehensive victories for activists, we find that activists were successful in mobilizing large numbers of employees, generating significant media attention, and forcing employers to engage in some types of substantive organizational change. Taken together, our findings reveal that scholars of social movements and organizations can gain analytical leverage by expanding their views of opportunity structures; focusing on employee activism as more of a dynamic, negotiated process; and defining activist success along multiple dimensions in the context of corporations.