Previous research has consistently found relationships between union loyalty and the antecedent variables of demographics, job related variables, and union related variables. However, little or no research has investigated the relationship between union loyalty and individual dispositions and organizational context. The purpose of this study was to test a causal model which evaluated the influence of individual dispositions and organizational context in predicting union loyalty controlling for the effects of demographics, job related, and union related variables. Contextual data were collected from 405 schools and matched with union loyalty and other attitudinal data from 838 public school teachers in a large U.S. Midwestern city. The LISREL results indicate that the individual dispositions of positive and negative affectivity and the contextual variables of attendance rate, school type, race homogeneity and socio-economic status had significant total causal effects on union loyalty. Implications of these findings are discussed.