Turners & Growers has challenged Zespri over the commission it charges kiwifruit growers for its services.
The fresh produce company is campaigning to end a near-monopoly held by Zespri on kiwifruit exports.
It has issued a 2007 draft report from the specialist consultancy firm Grant Samuels which it says is highly critical of Zespri's practices in setting its margins and allocating costs.
Turners has questioned why Zespri and the kiwifruit growers organisation, which commissioned the report, have not disclosed it to the growers.
The report analyses Zespri's performance in setting its margins over three years from 2004 to 2006.
Turners & Growers chief executive Jeff Wesley says the findings and criticisms are still relevant.
Zespri services director Carol Ward disputes the accusation that the company is not being transparent in its dealings with growers.
She says the Grant Samuels report was used by the industry to consider whether the margins were appropriate but its figures are out of date and no longer relevant.