The article examines the role of library union, Chicago Public Library (CPL) Local 88, in the development of the CPL in Chicago, Illinois, in 1937-1952. Based on the published newsletters and records available in the Chicago Public Library Municipal Reference Collection, Local 88 had carried out strategies to strengthen the weakening civil service practice within the CPL, improved educational opportunities for staff, and provided cultural and social events for employees. In addition, the union led to the development of a new moral model for public librarianship and rejected the patronage process of professionalism.