In an effort to comprehend activism toward corporations, scholars have proposed the concept of corporate opportunity structure, or the attributes of individual firms that make them more (or less) attractive as activist targets. We theorize that the personal values of the firm's elite decision makers constitute a key element of this corporate opportunity structure. We specifically consider the political ideology, or conservatism vs. liberalism, of the company's CEO as a signal for employees who are considering the merits of engaging in activism. As an initial test of our theory, we examine the formation of LGBT employee activist groups in Fortune 500 companies in the period 1985-2005, during which the formation of such groups was generally perceived to be risky for participants. Using CEOs' records of political donations to measure their personal ideologies, we find strong evidence that the political liberalism of CEOs influences the likelihood of activism. We also find that CEOs' ideologies influence activism more strongly when CEOs are more powerful, when they oversee more conservative (i.e. less liberal) workplaces, and when the social movement is in the early phase of development. In supplemental analyses, we examine instances of recent CEO succession, showing that a new CEO's liberalism relative to the predecessor CEO especially heightens the likelihood of activism. Our theory and findings contribute to research on social movements, corporate stakeholders, and upper echelons. We identify promising future research opportunities in each of those areas.