The Chief Ombudsman has recommended the Christchurch City Council reveal how much it paid to host the Ellerslie Flower Show.
The ruling follows a request made by Christchurch newspaper The Press.
The Ellerslie International Flower show was held in Christchurch for the first time this year, after being purchased for an undisclosed sum in November 2007.
Christchurch Mayor Bob Parker says it is unfair that other councils in New Zealand are not forced to disclose the same sort of information, which is usually kept secret due to commercial sensitivity.
Mr Parker says the show brought at least $20 million directly into the Christchurch community when the world was in a recession.
The city council will debate the issue behind closed doors in two weeks' time.
The event was previously held in Auckland for a number of years.
