Video of a confrontation between Labour Mt Roskill candidate Michael Wood and the husband of National Party rival Parmjeet Parmar has emerged.
The "robust exchange", in Mr Wood's words, took place at a heated by-election debate on Wednesday night.
Mr Wood says the video proves claims he attacked Ms Parmar's husband, Ravinder Parmar, were "a proven lie, completely made up".
"We're calling for this kind of negative campaigning, these kinds of lies, to stop so that our campaign can just focus on the issues," he told Newshub on Saturday.
It's believed Mr Wood took exception to comments about his wife from National supporters seated in the front row, which included Mr Parmar.
Ms Parmar said Mr Wood "absolutely overreacted" and his "response was disproportionate". National Party member Graham Collins accused Mr Wood of "manhandling Mr Parmar, threatening him".
"He had his arms around Mr Parmar, physically. He definitely had him in some sort of hold."
Mr Collins then said Mr Wood called him a "mother****r".
When spoken to by Newshub on Saturday morning, Mr Collins hadn't seen the video but said he stood by his claims. Newshub has been unable to reach him since.
The entire confrontation, from the time Mr Wood stands up to when he turned away, lasted 14 seconds. Mr Wood said the allegations against him were "quite a serious act of slander".
"Their campaign and John Key need to condemn that behaviour and make a rock-solid commitment that it won't happen again," he told Newshub.
"This is toxic, Trump-style electioneering. It has no place in Mt Roskill and no place in New Zealand."
Police told Newshub an Indian man was escorted out of the building afterwards, but it wasn't Mr Parmar.
Mr Little says Mr Key needs to clean up his party's act.
"It's his candidate, and his candidate's team, that have acted in a way that is totally out of order. It's old-fashioned National Party dirty politics, and we don't need it here."
Mr Wood told Newshub on Friday he was just defending his wife.
"I love her; she does amazing work, and I will certainly defend and stand up for her if she's attacked by my opponents in a pretty gutter way."
Mr Little defended Mr Wood's behaviour, saying "you don't draw family into political campaigns".
"Parmjeet Parmar and her campaign have broken that rule. They're going to have reconcile that with their conscience."
Campaign chair Steven Joyce says Ms Parmar and the National Party are focused on "campaigning positively".
"It's Mr Little who appears distracted by this issue and attempting to re-write history. He seems to be feeling the pressure."
The by-election, forced by Phil Goff's election as Auckland Mayor, will take place on December 3.