Studies of work/life balance have focussed on offline settings, and even though technology is considered as a boundary‐influencing feature, social media have not been the focus. Social technologies challenge the relationship between work and private life in new ways, due to their identified affordances: visibility, persistence, association and editability (Treem and Leonardi, 2012). In this paper, we present the results of a study of social media use (Facebook and Twitter) by employees of non‐governmental organisations (NGOs), and show how, through their affordances, these technologies influence the relationship and boundaries between work and non‐work, increasing visibility and reducing individual privacy. Consequently, we observe boundary work tactics that aim to protect private life from both public and professional scrutiny, in prohibitive, reactive or active ways. Our results call for organisations to develop explicit policies or guidelines for social media use, in both their own interests and those of their employees.