A landlord cannot simply change the agreed rent during a fixed-term lease. An increase may be possible if the tenancy agreement allows a review and the landlord follows the applicable rent-control rules, including limits on how often rent can be reviewed and the required notice period. Check your lease and the RTB’s current guidance, as the rules can depend on when the tenancy began and the property’s circumstances. If you believe the increase is unlawful, the RTB or a solicitor can assess the individual facts.