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 flownto 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.
The scandal has led to conflict-of-interest accusations against her.
She is a close personal friend of Oravida owner Deyi Shi, and the company has donated $56,600 to the National Party and entertained party MPs and Cabinet ministers.
Mr Pulman is a Papakura community leader and businessman whose HEB Construction is based in Ms Collins' electorate.