This study examined differences between union and non-union construction workers in terms of safety performance and of demographic, employment, and sociopsychological factors related to safety performance. Data were collected by questionnaire in a larger study on construction workers' safety practices among 384 workers employed at nine nonresidential construction sites in the Baltimore metropolitan area. Union and nonunion construction workers differed in terms of safety performance and certain factors related to safety performance. Higher safety performance scores among union workers were, however, related to the fact that union members were older than nonunion members. Moreover, other differences were related to elements over which unions have more control. Findings revealed the need of special attention of the nonunion youngest members, and of additional evaluation of the actual and potential role played by unions in occupational safety.