Such a third party can be either a single arbitrator, or a board consisting of a chairman and one or more representatives. Arbitration is often used to settle major grievances and for settling contract interpretation disputes. Voluntary arbitration is that agreed to by the parties without statutory compulsion.
Compulsory arbitration is that imposed by law.
Governments sometimes impose it to avoid strike or to end one. Normally the result of collective bargaining is a written contract which covers all employees in the bargaining unit, both union members and non-members. By contrast with arbitration the mediator, conciliator or conciliation board does not bring in a binding award and the parties are free to accept or to reject its recommendation. The conciliator is often a government official while the mediator is usually a private individual appointed as a last resort, sometime even after the start of a strike. A trade union which organized on the principle of limiting membership to some specific craft or skill, i.e., electricians, plumbers, etc.