This systematic literature review examines how teacher unions frame professionalism discourses within contemporary socio-political contexts. By synthesising insights from international empirical research, the study explores the roles teacher unions play in challenging neoliberal education reforms that emphasise standardisation, accountability and external controls. It highlights the dual role of unions as both professional and industrial advocates, showcasing their efforts to promote teacher autonomy, professional status and collaborative practices. The analysis identifies five key themes: the de-professionalisation of teaching under neoliberalism; the collective agency of unions; complex relationships with governments; the pursuit of public legitimacy; and the intertwined nature of unions' professional and industrial roles. This review contributes a conceptual framework for understanding teacher unions' discursive, relational and contextual strategies in shaping professionalism. It underscores the need for further research into unions' constructive roles in fostering democratic professionalism and advancing equitable education reforms globally.