Although technically not considered to be termination for just cause, the legal effect can be the same if an employee, due to illness or disability or other independent intervening cause, is unable to return to work for an unduly lengthy or indefinite period of time. In such cases, the employment relationship is said to be legally "frustrated".

There is no predetermined dividing line defining the exact point as to when the employment relationship can be said to be frustrated. The point when frustration occurs cannot be unilaterally determined by the employer. The event constituting the frustration of the employment relationship occurs independently of the will of the parties, and all the circumstances must be examined, including the nature and history of employment.

There may be human rights considerations as well. An employer may be required to accommodate a disabled employee who is unable to return to work due to disability.