Do I have to use vacation if I am on leave due to temporary shutdown/my unit closing for a time?

If you are on leave due to a temporary shutdown, this leave is at the employer's request, so you do not have to exhaust vacation.

If you are employed in a unit which regularly closes down or reduces its operations for a specific time period of up to three months, you may be granted a leave of absence during these periods if it is agreed that you will return to work at the earliest date your services are required. You will not be required to exhaust your vacation or sick leave to obtain a leave of absence for this reason.