If the landlord has a valid reason (as allowed by the RTA) for entering your unit, you cannot refuse to let the landlord in. If you don’t let the landlord in, the landlord can give you a notice of termination claiming that you are interfering with their lawful rights and you could be evicted. Also, interfering with a landlord’s lawful right is an offence under the RTA.

Source: www.sjto.gov.on.ca