Deputy Prime Minister Winston Peters provided consular assistance to one of the "Bad Boys of Brexit" a month before he "scoffed" at claims they had been dispatched to New Zealand to help with NZ First's campaign.
He is being accused by National of "using his ministerial influence and taxpayer-funded staff to help ease the way" for Aaron Banks to travel.
But Peters denied this, saying providing consular assistance was part of his role as Foreign Affairs Minister.
Emails, obtained under the official information act (OIA), show Aaron Banks contacted Peters' office seeking help in relation to a transit visa for Australia.
Those emails show Banks was due to leave Auckland to go to Melbourne on June 16.
It is not known when Banks got to New Zealand – borders have been closed to non-New Zealanders since March.
But a spokesperson for Peters said he had "no involvement in Mr Banks' presence in New Zealand".
"Mr Banks had his own personal reasons for travelling to New Zealand prior to this date."
The spokesperson also denied NZ First had hired Banks' "crew" to help with NZ First campaign.
In a letter responding to the OIA, Peters said "consular assistance was provided to Mr Banks".
"That is consistent with my ministerial office's actions throughout this Government, where we offer assistance to those who encounter difficulties with emigration, and subsequently contact our office."
But National's foreign affairs spokesman Simon Bridges was not convinced.
"To claim this is simply a normal example of consular assistance is nonsense."
Bridges said it was "rare and notable" that a Foreign Minister was called upon to help provide consular assistance – something he said was usually dealt with by the Ministry of Foreign Affairs.
But a spokesperson for Peters said: "The Deputy Prime Minister is contacted by a large number of individuals requesting assistance with matters outside of his portfolio.
"As Foreign Minister, there is often the perception he can assist individuals with their visa arrangements with foreign countries. In this instance, as with other cases, Mr Banks was referred to the correct contact for his issue."
The emails show Peters' senior private secretary provided Banks with the contact information of an Australian Home Affairs Office after he expressed concern at his ability to get a transit visa in Melbourne.
She told Banks to: "Let me know how you get on."
But Banks was granted the visa before contact with that official was made, the emails show.
Some 26 days after Bank's contact with Peters' Ministerial office, Peters "scoffed at suggestions that a team of six political operatives have been dispatched to New Zealand to assist his campaign," according to a NZ First media statement on July 7.
"Not only have I not hired such a crew but it is impossible to see how they would even gain entry into the country".
He did not, however, deny Banks, and his colleague Andy Wigmore's, involvement in NZ First' campaign.
Neither did they, in an interview with the Nation.
In a statement today, Peters' spokesperson said his statement stands.
"No 'crew' were hired, nor brought into the country."
Wigmore and Banks dubbed themselves the "Bad Boys of Brexit" because of their involvement in the UK's Leave campaign in the lead-up to the Brexit vote.
Banks told the UK's Telegraph in July: "I'm going to be on ground in New Zealand causing trouble – mischief, mayhem and guerrilla warfare in the New Zealand election".