Businesses face mounting pressure from societal groups to deal with critical social and environmental issues. Inside organizations, this translates into the formalization of CSR policies and roles, as well as employee activism coming from outside official channels. Little is known, however, about how those two types of insider social change efforts interact. Drawing on the concept of boundary work, we conducted a qualitative study of five cases of environmental employee activism within five MNCs, where employees formed bottom-up networks outside formalized CSR and raised thorny issues. From a longitudinal analysis, we induced a four-stage model whereby 1) employee activists first contested CSR’s symbolic boundaries, 2) which led them to breaching CSR’s jurisdictional boundaries, 3) before being channeled by the organization, 4) and finally fitting in and overflowing redrawn CSR boundaries. Our analysis contributes to the literature on insider social change agents by unveiling how institutionalized CSR acts simultaneously as a resource provider and a gatekeeper for employee activism.