Background: UPnGO is a web and mobile physical activity program developed by ParticipACTION to help Canadians sit less and move more at work. The program's goal was to assist employees with increasing steps through goal-setting and the provision of real-life team challenges and rewards. However, the program cannot change employee behaviour if it is not adopted. The COM-B model and the Theoretical Domains Framework(TDF) offer a systematic method for understanding barriers and facilitators to the adoption of UPnGO. Objective: To conduct a behavioural analysis of barriers and facilitators influencing employees' potential adoption of UPnGO. Methods: Six focus groups with employees were conducted by a market research firm. Barriers and facilitators mentioned by employees to adopting UPnGO were extracted by a research assistant and were independently coded by two researchers using COM-B and the TDF (72% agreement). Results: 407 barriers and facilitators were extracted. Most prominent factors considered to be influencing employees were: physical opportunity(45%), reflective motivation(25%), and social opportunity(20%). Employees had mixed feelings about UPnGO features (e.g. incentives, apps), and variable access to equipment (e.g. standing desks, fitness trackers) and wanted employers' permission to be active during the work day. Conclusions: The behavioural analyses identified important recommendations for refining UPnGO. It may be important to provide employees with explicit permission, equipment and time to use the program, opportunities to tailor features, and autonomy to choose rewards. These recommendations were integrated to varying degrees in the implementation of UPnGO. Further research will examine whether recommendations improved uptake of the program.