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.
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.
In August, Mr Key visited Mrs Collins' electorate and was taken to two businesses - a local pharmacy and HEB Construction.
Mr Pulman spoke about the company supplying Oravida and produced a bottle to show Mr Key.
A spokeswoman for Mr Key said he had visited knowing the company supplied Oravida, and was "comfortable" having done so.
"He was interested in the raw milk production process, and was aware the company supplied milk to Oravida."