Teacher unions worldwide are being criticized for disregarding their responsibility as professionals towards education and students. Critics have claimed that teacher unions tend to protect incompetent teachers, place their own needs and interests above their students, and continuously demand for financial increases even when there is more urgency to elevate teacher professionalism and improve teacher quality. This statement does not take into consideration the political, social and economic aspects that influence unions' decisions. Therefore, this study utilizes a qualitative research design, specifically a grounded theory approach to investigate the challenges facing teacher unions in Lebanon from the perspective of union leaders and union members. Data was collected from seventeen public school union leaders and twenty-one teachers. Findings have revealed that teacher unions have assumed a social justice role limited to raising awareness. There are organizational, legal, political, educational, social, and economic barriers that prevent teacher unions in Lebanon from assuming a more active role as a union.