While the current literature generally assumes that implementing sustainable business practices (SBPs) will lead to improved wellbeing and positive outcomes, relatively little research has explored the potential tensions and conflicts that SBPs may cause in multi-actor networks. To address this issue, we conduct a qualitative multiple case study in a regional business network, including interviews with 43 managers in 17 firms in different industries. The findings of this study identify four types of tensions (economic, structural, psychological, and behavioral) that tend to emerge when firms implement SBPs in networks, and illustrate how different stakeholders (implementers, suppliers, customers, other network partners) perceive them. Overall, this study contributes to the current literature by highlighting the underexplored "dark side" of sustainability, and illuminating how organizational decisions aiming at improving collective wellbeing can also lead to tensions and conflicts. For managers, this study offers insights into how to anticipate, manage and mitigate potential tensions that might arise in business networks when one stakeholder decides to implement a SBP.