Tenants must write to the landlord and confirm that they both agree with the rent change. If the landlord agrees to the change in the tenancy, a new lease must be signed. If a tenant violates the terms of his agreement, the lessor can act against him. The owner may apply to the court for an order of ownership of the property. So far, legal education has been the subject of controversy over whether this legal suite applies even when the lease has been concluded, but the lease has not yet begun and the tenant has not yet moved into the leased property. This issue was settled by the Bundesgericht in its decision BGer 4A_393/2018 of 20 February 2019, which upheld the decision of the Zurich Commercial Court HG160080-O of 15 May 2018 (Altenburger AG acted legally + taxed as a representative of one of the parties to the proceedings).