Deputy Prime Minister Winston Peters has labelled National MP Tim Macindoe a "dysfunctional geriatric" for calling him a "rat" in Parliament today.
The house debated and passed the law to limit foreign donations to $50.
Mr Macindoe criticised Justice Minister Andrew Little for not having a select committee process for the bill and for only having a foreign donation limit for general elections.
Mr Little later told the House he had expected the Justice Committee to have completed the inquiry into the 2017 election.
"That has not happened," he said.
He added the Electoral Commission advised him any statutory changes needed to "have advance notice well in advance of the election and well in advance of the regulated period".
Mr Macindoe then spoke about why the Government were pushing the legislation through urgency and called Mr Peters a rat.
"I won't have a dysfunctional geriatric call me a rat, and I'm asking him to apologise," Mr Peters replied.
"He can't get away with that. Why didn't you stop him? If you're doing your job properly," he asked chair Anne Tolley.
Ms Tolley told Mr Peters he was "getting a bit close to the bone".
"There was an aspersion cast, and probably unparliamentary, but, unfortunately for the member, he just responded, so it's one all," Ms Tolley said.
Later today during Question Time Mr Peters told another MP to "take a Valium".