Westland Milk's biggest shareholder, Southern Pastures, said it would abstain on the vote called to decide on whether the co-operative can be sold to China's Yili.
Southern - an investment fund - said the move would allow West Coast farmer-shareholders to decide its future.
Hokitika-based Westland said in March that it had signed a conditional agreement for the sale of the co-op, which will see the Chinese dairy giant pay farmer-suppliers $3.41 a share. The deal is worth $588 million.
Westland will seek shareholder approval for the proposed transaction at a special shareholder meeting in July.
Southern, which has former All Black Graeme Mourie as one of its principals, owns 5.5 per cent of the co-op, which would be worth $13.6 million under the offer.