Can workplace custom or conduct override the written terms of a contract?

Workplace custom or conduct cannot usually override the written terms of a contract. The courts will tend to enforce the contract as agreed. The contract does not have to be fair or reasonable. An employer that wants flexibility must build this into the contract. Neither employer nor employee should assume that conduct contrary to the contract terms will change the contract. Conduct or custom can fill in gaps in the contract but cannot override contract terms. However, it is possible (albeit rare) for custom to override written terms if, for example, it has been customary for many years to ignore a written term such that employees have come reasonably to expect it to be ignored.