Why landlords ask
Landlords sometimes ask for a SIN to run a credit check, but every major credit bureau can perform a credit check with name, address, and date of birth alone. The SIN is not required.
What to say
Politely decline and explain that privacy commissioners have consistently found SIN requests excessive.
Offer to provide a reference letter from your employer, proof of income (paystubs, T4), and bank-verified rent payment history instead.
If the landlord insists, walk away. There are many landlords who do not require a SIN.
If you already gave your SIN
Ask the landlord in writing to destroy it once a rental decision has been made. You can also file a complaint with the applicable privacy commissioner if you have privacy concerns.