Using a sample of 1,468 private sector establishments, this article addresses the relationship among part-time workers, commitment-based human resource (HR) systems, and establishment financial performance. Building on theoretic perspectives about equity perceptions and reciprocal exchanges, we find that the proportion of part-time workers in an establishment workforce is nonlinearly related to establishment financial performance in an inverted U-shaped relationship. In addition, the interaction between part-time workers and commitment-based HR systems is negatively related to establishment performance. The analysis suggests that those deciding about how to structure establishments’ workforces should consider how interactions between different types of workers within workforces can influence establishment performance.