It depends whether the person staying is a guest or a sub-tenant. It is all about what rights you are seeking to give that person.
Having guests stay over is part of your right to quiet enjoyment and exclusive possession of the property under standard residential tenancy terms 52 and 53. However, under clause 53, your right to exclusive possession can be limited if you agree in writing to limit it. Even so, the Tribunal has indicated that if your lease limits the total number of residents, this restriction may need to be endorsed by the tribunal to be enforceable, particularly if it is affecting other rights and even perhaps discriminating against you. See our FAQ: Extra terms and standard leases – what terms are enforceable?
Your right to quiet enjoyment should also include a right to live with your spouse, de facto, or close family member. This includes children and having a baby. Your right to privacy means that you shouldn’t have to tell your landlord or agent every time you start a new relationship or someone stays over. If you are having a guest to stay, there is no requirement to tell the landlord or agent, or ask for permission.
However, you do need written permission from your landlord or agent if you want to have a sub-tenant live with you (clause 72). If you don’t have written permission for a sub-tenant to be there, you are in breach of your lease and the landlord could issue you with a notice to remedy and then apply to the Tribunal for an order that the person move out, or they could serve a notice to vacate, if you didn’t vacate they could make an application to the Tribunal for an order terminating the tenancy (the Tribunal may order termination or decide this does not warrant termination and order that the person move out.
When does a guest become a sub-tenant?
A guest usually becomes a sub-tenant or occupant when they pay rent or contribute money, particularly if they pay a set amount on a regular basis. They are also more likely to be a sub-tenant if the premises are their only residence, if they have a key, direct their mail to your address, help care for the property, or arrange to stay for a long time.
Another test is whether you intended to create a legal relationship. If the visitor thinks they have a right to stay, and you think the visitor has to pay you rent, they are probably a sub-tenant.