Dealing with mould issues in a rental property can be a bit challenging, and it doesn’t help that the law does not set out clear guidelines on how to deal with this type of situation. The first step for you would be to meet with your tenants and try to come up with a plan on how to deal with the problem. If they have to move out temporarily while you get the problem corrected, you should offer them a rent rebate for the time that they’re out of the unit, or offer to pay for their accommodation costs. It is really up to both parties to work something out. If they chose to move out instead and terminate their tenancy, then you should both sign an Agreement to Terminate the Tenancy which is a Form N11, this form can be obtained from the Landlord and Tenant Board’s website at https://tribunalsontario.ca/ltb/forms/