This dissertation explores the impact of data-driven approaches to worker advocacy. I combine historical and design research, organized around a case study of management-engineering projects conducted by the International Ladies Garment Workers Union (ILGWU). I survey how workplace data been used to advocate for US workers in the past, how the decisions and challenges of using data to represent worker perspectives map onto analogous methodological challenges that impact the design of workplace measurement analytics today, and how these design techniques and insights from the past can be be applied in present-day workplace advocacy for workers in data-driven workplaces. I conclude with key trade-offs in relying on worker data and data expertise for worker advocacy