Using a social-ecological framework, we drew on a targeted literature review and historical and contemporary cases from the US labor movement to illustrate how unions address physical and psychosocial conditions of work and the underlying inequalities and social determinants of health. We reviewed labor involvement in tobacco cessation, hypertension control, and asthma, limiting articles to those in English published in peer-reviewed public health or medical journals from 1970 to 2013. More rigorous research is needed on potential pathways from union membership to health outcomes and the facilitators of and barriers to union-public health collaboration. Despite occasional challenges, public health professionals should increase their efforts to engage with unions as critical partners.