Recent union-supported teachers’ walkouts and strikes across several U.S. states and cities highlighted union-led and grassroots efforts to amplify teachers’ voices. Yet, the recent U.S. Supreme Court decision, Janus v. AFSCME, Council 31, provides a strength test for teachers’ unions and members engaging in social justice/equity work within a post-Janus landscape. This article first explores traditional functions of teachers’ unions. Next, it examines Janus and potential consequences for union participation, teachers’ advocacy, and civil rights. Using a social justice lens, the article discusses how and why unions may need to consider strengthening “social justice unionism” by building on walkouts and strikes.