U.S. workers’ views of unions have warmed notably in recent years, even as membership rates remain near historic lows, raising the reality of a sizable “representation gap” that persists between union interest and union coverage. This study examines how justice perceptions relate to union beliefs and intentions. A cross-sectional survey (N = 600 U.S. workers) was conducted with balanced groups (300 union / 300 non-union). The methods workflow included LASSO network analysis, Confirmatory Factor Analysis (CFA), and Structural Equation Modeling (SEM) using multi-group invariance testing. Distributive Justice and Union Instrumentality were combined into a joint construct: Justice–Instrumentality (JI). Procedural Justice (PJ) had a strong positive effect on Justice–Instrumentality (JI). Both Justice–Instrumentality (JI) – Union Orientation (UIO) and Procedural Justice (PJ) – Union Orientation (UIO) were found to be non-significant. The core contribution of this study is the discovery of the Cognition-Action Gap, with the implication that procedural fairness is necessary but not sufficient to drive union-oriented behavior.