A Social Insurance Number (SIN) is necessary for all Canadian citizens, permanent residents (PR), and temporary residents in order to work in the country or benefit from government services and benefits. You will be given a temporary SIN if you are a Temporary Foreign Worker (TFW) in Canada. Your SIN will begin with the number nine and will expire on the same day as your work permit expires. An international student must also have a SIN if they want to work part-time while attending classes.