SIN

Employers are required by law to request each new employee's SIN within three (3) days after the day on which their employment begins, and maintain a record of the SIN of the employee.

Employers must ensure that employees with a SIN beginning with the number "9" are authorized to work in Canada and have a valid immigration document. 

For more information on SIN Code of Practice visit:
https://www.canada.ca/en/employment-social-development/services/sin/reports/code-of-practice.html

International students wishing to work in Canada may obtain a Social Insurance Number (SIN) from Service Canada. Service Canada recommends that students apply in person for the card and allow three weeks for processing. Employers must ask to see the SIN card of all new employees as soon as they are hired. The employee must apply for a SIN within three days of the start date of employment and may work during the waiting period.

For more information on obtaining a SIN visit:
http://www.servicecanada.gc.ca/en/sc/sin/index.shtml