After providing some background data on the number of blue-collar and white-collar employees covered by collective bargaining agreements at U.S. institutions of higher education, this study used data from a 1997-1998 study on the costs of staffing in higher education. It was conducted by the Association of Higher Education Facilities Officers (APPA) and other sources to estimate models that explain the variation in academic institutions' salaries for a number of narrowly defined blue-collar and white-collar occupational groups. The focus was on nine occupations for which at least 115 institutions in the sample reported both an occupational salary level and whether the employees were covered by a collective bargaining agreement. When the analysis treated collective bargaining as exogenous, estimated union/nonunion salary differentials were found in the range of 10% to 17% for the occupations in the sample. When full professor salaries were removed, the differentials increased by about 3 percentage points. When collective bargaining was treated as endogenous and the union/nonunion differential was estimated using an instrumental variable approach, the differentials rose into the 15% to 40% range, roughly what the unadjusted mean differences were in the sample in the salaries of staff covered and not covered by collective bargaining agreements. These estimates, however, were higher than previous estimates of the impact of unions on their members' relative salaries. An appendix contains the occupational descriptions. (Contains 4 tables and 13 references.) (SLD)