The RTA stops a landlord from changing locks without handing over a key — it doesn't spell out the reverse, but your right of entry doesn't disappear because the key did.
Short answer
Ontario's RTA doesn't contain a standalone rule banning a tenant from re-keying a unit. What it does contain is section 24, which stops the landlord from altering the locking system without giving the tenant a replacement key, and sections 26-27, which give the landlord a right to enter with proper notice regardless of whose key currently opens the door. Put those together and a tenant who changes the locks without providing access is functionally blocking a right the RTA still gives you.
Interpretation Guideline 6 confirms the rule runs landlord-to-tenant: the Act prohibits "a landlord from altering the locking system on a door giving entry to a rental unit or residential complex…without giving the tenant replacement keys." A landlord can still change locks during a tenancy — "so long as the tenant is given a key to the new lock and is not charged for it." After a tenant permanently vacates, or once the sheriff enforces an eviction order, section 39 lets the landlord change the locks freely.
Nothing in the guideline states a parallel prohibition on the tenant's side. That said, this is where inference has to be labelled as inference rather than a section number: the landlord's right of entry under sections 26 and 27 — the 24-hour-notice, 8 a.m.-to-8 p.m. right covered in the entry-notice rules — is a right against the unit, not against a specific lock. A tenant re-keying the door doesn't suspend that right; it just makes it physically impossible to exercise without the tenant's cooperation. If a landlord shows up with valid 24-hour notice for a legitimate reason and can't get in because the locks changed and no key was provided, that's a live dispute about obstructing a lawful entry right, not a settled question the Act answers with a section number.
The cleanest way to avoid the dispute entirely: most tenancy agreements should address it directly — a tenant who re-keys for a genuine safety reason (a breakup, a lost key, a security concern) providing the landlord a working copy resolves the entry problem without anyone needing to argue about it. Where it isn't resolved and access stays blocked, it tends to surface as part of a broader dispute at the Board rather than a stand-alone application — see the LTB timeline for how long that kind of dispute actually takes to resolve once it's filed.
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