Understanding how support structures influence job outcomes in the context of enterprise system (ES) implementations is important if we are to advance the rate of success of such implementations. This paper examines how support structures—conceptualized as formal support structures (FSS) and informal support structures (ISS)—affect job outcomes in the shakedown phase of an ES implementation by drawing on the job strain model. Prior research on the job strain model suggests job characteristics (i.e., job control and job demand) and social support together affect job outcomes. A model of these effects on three post-implementation job outcomes (i.e., job stress, job satisfaction, and job performance) is developed. Data were obtained from 152 employees in a longitudinal field study at a large multinational firm. Results show that FSS do not have a direct influence on job outcomes, but interact with job demand to influence all three job outcomes. ISS have direct and interaction effects on all three employee job outcomes. The effect of FSS and ISS on employee job outcomes is mediated by job demand and job characteristics partially mediate the effect of ISS and FSS on employee job outcomes.