This research examines the impact of brands’ purchasing practices on suppliers’ shop floor labor conditions in global electronics supply chains. Through a case study of a second-tier supplier to Apple, the correlation analysis of matched attendance records with datasets of demand, production, and purchasing volumes and the qualitative findings via 51 stakeholder interviews and two months of participant observations as an intern at the supplier factory suggest that: The buyer’s highly volatile purchasing practices are the origins of labor violations in the forms of excessive overtime and extensive use of student interns. Meanwhile, the management systems of disconnected sourcing and compliance working mechanisms within the buyer itself impede the possibility of linking future sourcing decisions in tandem with compliance performance. These findings implicate that better labor conditions in global supply chains cannot be achieved without a fundamental change in buyers’ purchasing behaviors and working mechanisms of sourcing and compliance.