This study examines school leaders' implementation of collective bargaining agreements (CBAs) negotiated between teachers' unions and school district administration. Using interviews with school leaders and drawing on a structure-agency perspective, the research highlights the interplay between school leader decision-making, union power, and school social dynamics in CBA implementation. The findings demonstrate that school leaders employed diverse strategies to manage collective bargaining work rules that varied based on school leaders' tenure. Experienced leaders defrayed CBA disputes, while less experienced leaders deferred to teachers' interpretations. Our findings further illustrate how leaders leveraged CBA provisions in ways that privileged efficient school functioning.