Generally it is 2-4 years, with most employers waiting for 4 years so there is no doubt. It is considered on a case by case basis. “Frustration of Employment” is a legal principle that allows an employer to unilaterally terminate employment after a certain amount of time due to the employees inability to perform employment duties, even after reasonable accommodations. This principle will not necessarily apply if you are in a unionized employment. In those cases, the collective agreement will dictate the conditions under which employment can end.