The news item in question was entitled "Protecting Perks" and was broadcast on 16 July 2016 on Nine News Sunday.
The Australian Communications and Media Authority looked into the item that included claims that former Ku-ring-gai mayor, Cheryl Szatow and the Ku-ring-gai council had wasted money, including on a legal challenge to the NSW Government's plans to amalgamate Ku-ring-gai and Hornsby councils.
The probe was carried out after a complaint that the item was inaccurate, biased and unfair.
"The code requires that commercial television news programmes present factual material accurately, and do so in a fair and impartial way."
The news item was found to have inaccurately stated that the mayor had spent $900 a week on having flowers delivered to her office.
ACMA was advised that this figure referred to the cost of 30 separate deliveries over nine months.
Four other allegations of inaccuracy were found to have no basis.
Channel Nine has undertaken to inform relevant staff about the ACMA findings; and use the matter for future training of staff.