This study is aimed to assess the effect of labor union on human resource management functionrntaking the case of Ethiopian public organization, namely, Ethio Telecom(ET). As the studyrnintended to describe and explain the effect of labor union on human resource managementrnfunctions, a cross sectional descriptive statistics explanatory study design was used to executernthe study. Managers, supervisors and ET’s labor union members are the study population whornwere invited to participate in the study. Data was gathered using the questionnaire from 248rnrespondents (supervisors and employees of ET) who were selected using the stratified randomrnsampling technique. Besides, using well-structured interview questions, qualitative data was alsorncollected from purposefully selected human resource managers. Both descriptive statistics andrnregression analysis has been used to reach on the results. Accordingly, the study found out thatrnET’s labor union performs its service, representation and regulatory functions to a fairly largernextent. It was also found out that a small percentage (27.9%) of the variation on human resourcernpractices can be explained by the labor union’s involvement in carrying out its service,rnrepresentation and regulatory functions. The study concluded that labor union has significantrnimpact on the way human resource management function are performed. Finally, the studyrnrecommended the need for a strong and active labor union that will positively influence andrnimprove the practice of human resource management