Contrary to the assumption of relational inertia that is prevalent in much of the research on organizational change, I propose that intraorganizational networks are instead subject to transitory shifts when organizational change produces high levels of ambiguity for employees. I develop a theoretical account of how networks defined by formal, semiformal, and informal organizational structure change in response to heightened ambiguity. I argue that, when ambiguity increases, people will tend to (1) decrease communication with formal network ties that do not have a significant semiformal component, (2) increase communication with semiformal network ties that do not have a significant formal component, and (3) increase communication with informal network ties. Empirical support for these propositions comes from unique data- including 40 weeks of archived email metadata, the full roster of email distribution lists, personnel records, and qualitative interviews-that span the period before, during, and after an ambiguity-producing restructuring at a large information services firm. These findings contribute to research on organizational structure, organizational change, and social capital activation and also have implications for management practice.