What does seniority mean in a union that follows a seniority based system? Higher seniority determines how long one has been at that job and the company allowing them to have priority on job shifts and choosing tasks. The lower seniority, the less flexibility in your schedule. Higher seniority determines how long one has been at that job and the company allowing them to be paid a higher wage than lower senior members. The higher seniority, the more flexibility in your schedule