Moving Auckland's port would increase imports costs by more than $500 million a year, according to a new report.
Ports of Auckland released the study, which was carried out by NZIER, on Wednesday.
The findings show that if the port is moved out of the city and freight needs to be delivered to Auckland from more distant ports, the cost of imports could rise between $533 million and $626 million a year.
Debate over the city's port has been raging for years, though calls to move it to Northland have gained traction recently with former Prime Ministers Helen Clark and Sir John Key publicly backing the plan.
A campaign by Waterfront 2029 is pushing to move the port's used-car and container section by 2029.
But Tony Gibson, Ports of Auckland's chief executive, says the study's findings show that moving the port would have "multiple negative impacts", both regionally and nationally.
"Some people claim that closing Auckland's port would not increase prices, but this is not true," says Gibson.
"Currently, the price of imports through distant ports like Tauranga is kept low by competition. Think of it as the 'Gull effect' for ports. Just as opening a Gull petrol station lowers prices at stations nearby, having a port in Auckland keeps import prices low."
The report found that moving the port could lead to a dip in GDP of over $1.2 billion nationally.
Gibson also expressed concerns at the higher carbon emissions that would result from moving the port.
CO2 emissions could rise between 121,000 and 212,000 tonnes annually if the port is moved, according to the report.
"This does not seem to be in line with the aims of the Zero Carbon Act, nor does it seem wise given the urgent need to tackle climate change," he said.
Ministers will meet on Wednesday to discuss the matter further before the issue is taken up by Cabinet.
The Government has yet to make a decision on the move.