Please check out this link: http://www.cra-arc.gc.ca/firefighter/

As a volunteer firefighter or search and rescue volunteer, you may be eligible to claim a $1,000 exemption instead of the VFA or the SRVA. For more information, see Emergency services volunteers. If you choose to claim this income exemption, you will not be eligible for the volunteer firefighters' amount or the search and rescue volunteers' amount. The income exemption related to emergency services volunteers is shown in box 87 of your T4 slips.