This article assesses the use of social media in union communications based on an international survey with 149 unions affiliated with UNI Global Union. High expectations of union modernization, leadership and pressures from members are likely to drive the agenda of social media within unions. However, the actual use of different channels is based on organizational variables such as membership base and participation in communities of practice. Beliefs about the anticipated benefits and risks of social media were not found to be influential in these early assessments. Implications for union communication strategies are discussed.