Re:900 social insurance numbers stolen from Revenue Canada v...
by kitcar on Monday April 14, 2014 @01:50PM
(#7587670)
More specifically - you can't refuse to give your SIN to a financial institution or to your employer (as for 99% of Canadians those are their main sources of income, and because those entities need to submit information to the government regarding your income for tax purposes).
For most other things though you can refuse to disclose it (i.e. telecom providers, debt-only financial institutions like credit card providers)
People use all sorts of zany things to try to prove identity. I think public education is the first line of defence against the misuse of things like SSN/SIN.