Judith Collins' staff sought a briefing from Ministry of Foreign Affairs staff ahead of the "private" dinner she had with Oravida bosses and an unnamed Chinese border control official in Beijing last year.
Ms Collins has faced claims of a conflict of interest over the dinner given Oravida had previously sought Government intervention to overcome problems in getting its products into China, her husband serves on the company's board, and it has made substantial donations to the National Party.
In March Ms Collins acknowledged she was wrong not to tell Prime Minister John Key and the public of the dinner earlier and that in hindsight she should have treated it as part of the official business of the trip, and ensured it was disclosed in a Cabinet report on the trip.
More recently in the face of ongoing Opposition attacks, she has refused to answer questions in Parliament over the dinner saying it was private and she had no ministerial responsibility for it.
However documents released by the Ministry of Foreign Affairs and Trade this afternoon show that ahead of her October 2013 visit to China Ms Collins' staff sought a briefing from MFAT staff in the week before the October 20 dinner.
"We will require a briefing for the dinner", an unnamed staffer told two of MFAT's Northern Asia Division personnel on October 15.
An MFAT staff later notes in an email to Beijing that Ms Collins' office had changed its mind about the briefing, saying: "Nothing from MFAT is required. The Minister is having a private dinner on the Sunday evening."
Email exchanges between Ms Collins and MFAT staff show she wanted New Zealand Ambassador to Beijing Carl Worker to attend the dinner.
Mr Worker is shown asking whether an unnamed person, likely to be the Chinese official would be attending "the private dinner".
He was later told by an MFAT staffer that "your attendance is not expected or required".
Ms Collins has told the Herald Mr Worker asked her on the day of the dinner to inform him of anything of any significance that was discussed.
Labour MP Grant Robertson said, "it was clearly a dinner with an official of sufficient standing that she believed it required a ministerial briefing.
"I also note the comment that the official had 'agreed to meet the minister'.
"That clearly implies this was something that was being driven by the minister and Oravida."
"Judith Collins has tried to present this as a casual dinner with the friend of a friend. It was far from that. It was a dinner organised well in advance with an official who'd been asked to be there. That is not a private dinner."
NZ First Leader Winston Peters said it was "difficult to conceive of an event that could be less official than one to which the New Zealand ambassador is invited.
"Did Minister Collins want the ambassador at this dinner to impress a senior Chinese border official with how extensive milk company Oravida's 'pull' was with the New Zealand Government?" asked Mr Peters.
Ms Collins said her office "routinely asks for briefings for everything, even for Oravida".
"My office asked for the briefing for the dinner. When I found out I told them it was not to bother as it was a private dinner."
The documents also show that Ms Collins' visit to Oravida's offices in Shanghai on the same trip which she has previously described as "a cup of tea on the way to the airport" was well planned in advance.
Her office asked MFAT to make arrangements for the visit two weeks beforehand and the emails show MFAT staff went to some effort to schedule it.
"This was supposed to be a taxpayer-funded visit about justice issues, instead the minister used it to conduct multiple engagements to benefit her husband's compan," Mr Robertson said.
"John Key has done the right thing in demanding Maurice Williamson's resignation. It is time for him to ditch the double standards and make Judith Collins go."
But Ms Collins pointed out she had previously released the invitation to visit Oravida's office she received before she left for China.
"This is nothing new."
Labour's foreign affairs spokesman David Shearer said it was curious that MFAT released the information about Ms Collins' China trip so quickly.
"It looks to me as though (Foreign Minister Murray) McCully is the man who is going to be despatching Collins and pushing her over the edge. He's let the MFAT OIAs go out in a way that is very untypical of Murray McCully who normally hangs on to his OIAs as long as he possibly can."