The Ministry of Justice is investigating how a banner was hung from the bronze screen of the Supreme Court.
A man climbed onto the building and tied the banner to the bronze screen overlooking Lambton Quay on Thursday.
The ministry says it is not clear how the man got onto the screen surrounding the building.
Assistant deputy secretary Andrew Hampton says court security staff were onsite and police arrived quickly. A man was arrested.
Mr Hampton says the ministry is looking to see if any security changes are necessary.