Justice Minister Judith Collins arranged a meeting between a supplier to her husband's milk supply company and the Prime Minister.
John Key visited Green Valley Dairies owner Bruce Pulman in August last year during a tour of Ms Collins' Papakura electorate.
Mr Pulman's milk is bottled for Oravida and flown to China, where it sells for $23 a two-litre bottle.
Labour says the meeting between Mr Key and Mr Pulman illustrates the closeness with which Mrs Collins is associated with Oravida, in which her husband is a salaried director.
Ms Collins was placed on warning this week by the Prime Minister over her lack of openness about visits to the company during a trip to China.