Past practice, in labor law, refers to a practice that has been recognized and accepted by the parties and used several times in the past. It is sometimes the last resort for dealing with a grievance by considering the manner in which a similar issue was resolved before the present grievance was filed. Past practice is to be used as a definition of accepted behavior only by arbitrators to resolve a grievance when contract language is ambiguous or contradictory, or when the contract doesn't address the matter in dispute.
Such practice does not have to be written down in the labor agreement, but can arise on the basis of regular, repeated action, or inaction. Generally, the existence of the four following factors will indicate that a "past practice" exists: