Union officials often try to use "past practice" as a reason for preventing changes in working conditions from being implemented. A "past practice" is nothing more than the way things have always been done. 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, on your part.
Generally, the existence of the four following factors will indicate that a "past practice" exists:
1. The practice was clear and applied consistently.
2. The practice was not a special, one-time benefit or meant at the time as an exception to a general rule.
3. Both the union and management knew the practice existed and management and/or the union agreed with the practice or, at least, allowed it to occur.
4. The practice existed for a substantial period of time and occurred repeatedly.
Normally, you cannot stop an established and accepted "past practice" unilaterally. Rather, you must give notice to the union of your intent to do so and, if the union so requests, engage in negotiations to try to resolve any differences.