Many entrepreneurs start their businesses while staying employed. Although such businesses are theorized to have positive and negative effects on employers’ businesses, employers’ perceptions and reactions to subordinates’ entrepreneurial side businesses are mostly unexplored. Based on a vignette study of 988 managers, we find that employers acknowledge both opportunities related to increased job performance and job attitudes as well as threats emerging from enterprising employees. Employers’ prior experiences with enterprising employees make them perceive positive consequences as more likely. Situational factors affect the outcome expectancies and moderate the relationships between these outcome expectancies and employer behavior. We discuss implications of our findings for fostering entrepreneurial mindsets in established organizations and for the emergence of entrepreneurship.