Falloon hasn't commented on the allegations,other than to say he apologised for making unspecified mistakes,and had been getting mental health counselling.
In both cases,the allegations were first sent to the leaders of the opposing political parties,suggesting there may have been an element of politics at play.
But the developments also suggested that behaviour,which may previously have been accepted or kept quiet in the New Zealand Parliament,would no longer be tolerated.
Ardern said she learnt about the allegations on Tuesday afternoon and questioned Lees-Galloway about them in the evening. She said he'd shown a significant lack of judgment over the course of a year.
"He confirmed that a consensual relationship had occurred,that it involved someone who had previously worked in his office and had been based in one of his agencies,"Ardern said.
"Over the course of the conversation with the minister,it became clear to me that his position as a minister was untenable. I advised him of that at the time,"she said.
"In undertaking this relationship he has opened himself up to accusations of improperly using his office. He has not modelled the behaviour I expect as a minister that is in charge of setting a standard and culture in workplaces.
"His actions have led me to lose my confidence in him as a minister.”
Ardern said that,as she understood it,the relationship had ended several months ago.
She said the Parliament had long had a culture and an environment that needed improving. But she stopped short of saying the blame lay with male lawmakers.
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"We all have a role to make sure that we maintain standards in this environment,"Ardern said."I'm not going to start casting judgments on specific genders here."
Opposition Leader Judith Collins,leader of the National Party,said she wrote to Ardern on Wednesday saying the culture of Parliament needed to change and the two of them should work out how to achieve that.
"Parliament and these precincts are not always a safe working place. And it's not OK,"Collins said."And I believe she and I have an opportunity to fix it."
The Prime Minister's popularity has skyrocketed due to her response to the COVID-19 pandemic that has left the country largely unscathed,making her the favourite to win the election.
Her Labour Party,governing in a coalition with the Greens and the nationalist New Zealand First party,will face the National Party in what is expected to be a pandemic-dominated campaign.
But Labour has faced some turbulence in recent weeks.
Lees-Galloway is the second senior minister to leave Ardern's office this month,after health minister David Clark quit following slip-ups in the government's response to the pandemic and personal mistakes.
AP,Stuff,Reuters