American dairy interests are lobbying against Fonterra's proposal to allow share trading among its farmer shareholders.

In a letter to Agriculture Minister David Carter, the US Dairy Export Council, representing farmers and processors,  says the share trading proposal is a bid to lock in Fonterra's near-monopoly position in New Zealand to capture an unfair share of foreign dairy markets.

Some 10,500 dairy farmers who supply milk to Fonterra are voting on the share trading proposal, the third and final stage of the co-operative’s capital restructuring plan next week.

But the Minister of Agriculture has challenged the American claim that the New Zealand Government is backing moves by Fonterra to strengthen its hold on the domestic and international dairy trade.