COVID-19 created serious and long-lasting difficulties within educational systems resulting in higher rates of teacher attrition in the U.S. Teacher agency, which is the teacher's capacity to act professionally, is a predictor of teacher attrition. The school environment, through policies and practices, can inhibit teacher agency, and the constraint of agency promotes teacher attrition. As school structures shift to address new post-pandemic needs, there is an increased need to understand how school structures throughout the pandemic inhibited teacher agency and drove teacher attrition. We examine how school systems constrained the agency of three veteran high school teachers from March 2020 through their resignation in May 2022. The participants shared how their agentic constraints in the remote (reduced instructional time, optional student web cameras, changes to grading policy) and hybrid/in-person (addition of common assessments, administrative responses to new student behaviors) learning environments led to growing feelings of disenfranchisement and directly motivated their resignation. Campus administrators also experienced limited agency and could not effectively address the teachers' barriers during COVID-19. Implications are discussed.