Was the policy consistently applied over a period of time and did at least the majority of the employees have the opportunity to enjoy the practice. The longer the period of time a policy has been effect, the stronger the case for it being considered a past practice. Both the union and management know the practice has been in effect, and neither party has objected. There is nothing in writing either in the contract or in written company rules regarding the practice. Written language supersedes past practice.
Past practices are often difficult to establish.
Past practice grievances have became less common in recent years, as there are fewer practices not covered by work rules or contract language. For example, the NLRB has ruled that employer gifts such as a Christmas bonus or a Thanksgiving turkey are gratuities and cannot be considered past practice. Management's right to direct its work force and change operating procedures if it does not conflict with contract language has been upheld in numerous arbitrations. Furthermore, lax enforcement of a rule does not create an enforceable past practice. Finally, even if a past practice meets all of the criteria listed above, an arbitrator still may refuse to uphold the grievance.