What is Duty Of Fair Representation?

Legal Definition
The duty of fair representation is incumbent upon U.S. labor unions that are the exclusive bargaining representative of workers in a particular group. It is the obligation to represent all employees fairly, in good faith, and without discrimination. Originally recognized by the United States Supreme Court in a series of cases in the mid-1940s involving racial discrimination by railway workers' unions covered by the Railway Labor Act, the duty of fair representation also applies to workers covered by the National Labor Relations Act and, depending on the terms of the statute, to public sector workers covered by state and local laws regulating labor relations.
-- Wikipedia