The rules for each particular leave of absence are outlined within the region’s employment standards legislation, and each may vary slightly. Generally speaking, the employee must notify the employer in advance of their taking the leave, or if that is not possible, as soon as they are able to do so. This notice should be in writing, so that the employer has an official documentation that the employee is on leave.
For several types of leaves, employers will require an employee to provide documentation to confirm that they are eligible to take such a leave. In the case of a medical or disability leave for example, employers may require documentation from a physician substantiating the leave. This does not mean that employers will be entitled to confidential medical information like a diagnosis, but they are entitled to know how long your work will be affected for.