The NSW government is urging people to "dob in" unauthorised public housing occupants.
The move is designed to ensure tenants are paying the rent they should, which is based on household income, Family and Community Services Minster Pru Goward says.
Legitimate tenants will also have a two-month amnesty to declare unauthorised occupants.
Those who don't face eviction or will have to make back-payments on rent.
"Tenants who do the right thing and declare additional occupants will have their rent adjusted from the date of declaration, and will not be charged back rent," Ms Goward said in a statement on Sunday.
"However, tenants with undeclared occupants who do not take advantage of the amnesty will forfeit protection offered under the amnesty and risk being charged back rent."
She said random checks of 106 Housing NSW properties last year found evidence of undeclared occupants in 14 cases.
Tenants can submit declarations at www.housing.nsw.gov.au or make an anonymous report to the dob in line on 1300 468 746.
The amnesty will run from January 21 to March 17, 2013.