Fair representation is the principle that labor units must represent all of their members in good faith when then they represent bargaining parties. The union must act impartially, reasonably, without discrimination or malicious intent when following through on a grievance or new contract negotiation. The union must investigate a grievance to the best of its abilities by using the full official process.
This came about because of instances of racial discrimination by unions in the 1940s. After these events, the principle of fair representation became acknowledged by the Supreme Court in the United States. It is also known as the duty of fair representation.