Rio Tinto, the owner of New Zealand Aluminium Smelters, may have to pay higher annual charges to the operator of the port at Bluff, following an interim decision by an arbitrator.
An arbitrator was called in two years ago after the parties could not agree on the terms of a new 35-year agreement for the smelter to use the wharf. The smelter is South Port's biggest customer.
The interim decision points to an increase in annual charges payable to South Port, though a final contract is yet to be determined.
South Port says it's too early to say how the decision will affect future profitability.
Chief executive Mark O'Connor says a lot of the infrastructure used by the smelter needs increasing maintenaince, so there's been a need to ensure that the charges cover that.
Shares in South Port were unchanged at $2.55 on Friday morning