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http://www.servicecanada.gc.ca/en/si.../provide.shtml

<H2>When don’t I have to provide my SIN?

Some private-sector organizations may ask for your SIN. This practice is strongly discouraged, but it is not illegal.

Here are examples of when you don’t have to give your Social Insurance Number or show your card:

1. proving your identity (except for specific government programs)
2. completing a job application before you get the job
3. completing an application to rent a property
4. negotiating a lease with a landlord
5. completing credit card application
6. cashing a cheque
7. applying for a video club membership
8. completing some banking transactions (mortgage, line of credit, loan)
9. completing a medical questionnaire
10. renting a car
11. subscribing to long-distance or cellular telephone services
12. writing a will
13. applying to a university or college.

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