A study investigated the perceptions workers had of labor unions. Affiliation behavior and gender differences were employed as independent variables with respect to workers' attributions of trustworthiness in labor unions and their messages, as measured by the three dimensions of character, expertise, and dynamism of the Giffin Trust Differential questionnaire. All workers, 3,600 union members and 625 nonunion members, in a metropolitan postal district were surveyed. Data gathered from the more than 700 returned questionnaires revealed that affiliation behavior was the primary determinant of perceived trust in the labor union and its messages. Gender differences were also demonstrated to have a significant effect on attributions of trustworthiness, with union member males trusting the union on all dimensions to a significantly greater degree than union member females. These findings, however, were found to vary significantly according to affiliation behavior, with no significant differences in attributions of trustworthiness for male or female nonunion members. Finally, workers' attributions of trustworthiness toward the labor union were consistently higher than their attributions of trustworthiness toward labor unions' messages. (Copies of the questionnaire and its scoring key are appended.) (FL)