The duty of fair representation is incumbent upon U.S.labor unions.
Under the Taft-Hartley Act and subsequent amendments, unions were required to be held to standards of fair behavior somewhat analogous to those imposed on employers by the Wagner Act (National Labor Relations Act). One of the requirements, later extended by the National Labor Relations Board and the courts, was that unions represent all of their members fairly and impartially. One of the consequences of this requirement was that union funds be freely and fairly accounted for; prior to this there had been much financial secrecy at many unions and the existence of "slush funds" that were used at the discretion of the leadership of the union, sometimes for illegal purposes and sometimes to aggrandize themselves. While such practices were hardly totally ended, the requirement of open accounting made such practices explicitly illegal in and of themselves and as a consequence, more difficult for union leaders to engage in.
The duty of fairrepresentation is the obligation, incumbent upon U.S. labor unions that are the exclusive bargaining representative of workers in a particular group, to represent all those employees fairly, in good faith, and without discrimination.
The duty likewise does not apply for the most part to unions' internal affairs, such as their right to discipline employees for violation of the union's own rules or union officers' handling of union funds, which are regulated instead by the Labor Management Reporting and Disclosure Act.
Because the duty of fairrepresentation was originally created by judicial interpretation, however, rather than as an express stautory prohibition, employees covered by the National Labor Relations Act may sue their unions directly, without being required to first exhaust any administrative procedures provided under the National Labor Relations Board.