A well-known Baltimore labor arbitrator gave the audience this framework for understanding past practice.  

Decide first whether the past practice involves a benefit.  If it doesn’t, the doctrine probably doesn’t apply.  The obvious forms of a benefit are anything to do with compensation, shift times (because people organize their life around them), and working conditions.

When the practice touches more on a management right, the less likely the doctrine applies.  A supervisor allows employees to wear ear buds and listen to podcasts.  But then, a new manager decides there is a safety issue.  The early arbitration cases favored the practice which allowed employees to listen to their radios or bring their coffee to their work station.  But with ear buds which cancel out all other sounds, the safety interest and management’s rule is much stronger.  Employees might consider it a benefit, but it looks more like a management right.

The party arguing there is a practice bears the burden of proving the elements which are:  clear, consistent, repeated over a period of time, and mutuality.  The first two elements are easy to spot.  The third one is also not difficult to reach consensus:  just look at the number of times the practice was followed and how many times it wasn’t.  Whichever way it leans is the the answer on how binding it is.  

Mutuality is the fourth and more problematic element.  First, a practice usually develops at low levels, but enough so that the department head or the chief steward have apparent authority to bind their side.  Second, some practices arise out of a “gap” in the CBA.  Or the practice arises because the CBA is vague.  In these examples, the practice is often binding.  Remember the purpose of the CBA and the practice is to allow management and labor to get the work done.  (See more about that in #3 below).  Third, the real problem is when there is clear language in the CBA that contradicts an otherwise binding past practice.  It’s as though the parties were of one mind when they negotiated the contract, and another when they implemented the contract.

There are classic cases which illustrate this dilemma.  Here’s one such case.  We use this case because it shows that management can argue past practice, as well as the union, and expect the same result.  The contract (let’s call it Section A) provides for extra compensation.  But a practice develops that the payroll department does not pay it — because there’s already extra compensation under another contract provision (let’s call it Section B).  The payroll department’s practice meets all of the elements;  clear, consistent, over a period of time (years) and both supervisors (not just payroll) and union leadership knew (ie., mutuality).  Then, years later, someone in the union reads the contract and files a grievance.   Now, the arbitrator is faced with two undisputed facts:  there is clear language mandating the payment and a contrary practice.  Most arbitrators will enforce the contract language, and the employer must begin paying Section A, as of the date that the grievance was filed and going forward. Section B payment also continues because that was never in dispute.

It should be noted that not every case comes out this way.  Some (probably a minority of) arbitrators would enforce the past practice.  Their theory is this: there is no compelling reason to prefer contract language over a practice that meets all of the elements.  Bargaining and negotiators are imperfect, and reality sets in after the language is negotiated.  

Parties can prevent these disputes.  Put the practice in writing, such as a side agreement.  Or adopt a zipper clause which “zips out” any practices not memorialized in the current agreement.  Just be careful that when the current agreement goes into effect, the practice does not continue even for a day.  If it does, the parties have signaled to the arbitrator that the clause does not apply to that practice.  In the vernacular, the zipper clause is broken.

Finally, think about the relationship.  The business or agency has a mission.  The past practice doctrine is powerful because a binding past practice becomes a term of the CBA.  This makes sense because parties adopt practices to meet the needs of the business or agency.   It is always smarter to think of a binding past practice as though it were a provision in the CBA.

In the end, you can always negotiate for something else in the next contract.