Your neighbours can smoke in their private homes, unless they signed a lease or there are condominium bylaws that say they can’t. However, if second-hand smoke (tobacco or marijuana) from another unit is interfering with the reasonable enjoyment of your home, speak to your landlord.

If your landlord cannot resolve this issue, you can apply to the LTB using a T2: Application about Tenant Rights. You will be asked to show how the other tenant’s behaviour is clearly interfering with your reasonable enjoyment. The LTB determines each application on a case-by-case basis.

Source: www.sjto.gov.on.ca