Legal Talkback Landlord vs Principal Tenant

I am a landlord of a leased property. My tenant would like to lease out one room to a third party. Do I need to sign another separate contract with the new tenant?

Houses for sale and lease are advertised in the window of a real estate agent at Bondi in Sydney, Friday, April 24, 2009. (AAP Image/Tracey Nearmy) NO ARCHIVING Source: AAP