Act Party leader and Epsom MP David Seymour has been accused of fuelling prejudice after he sent a letter to constituents warning that tenants in a new housing development could have mental health issues.
Seymour stands by the letter, saying that the social housing development had a history of anti-social behaviour and he was "telling it like is".
Housing New Zealand (HNZ) has applied to the Auckland Council to replace a rundown residential building with a five-storey, 25-unit complex on Banff Ave, Epsom.
In a letter to residents, Seymour invited them to voice their concerns at a public meeting and said the development would put pressure on local infrastructure.
He added: "There is also a chance that some of the future residents will have social and mental health issues who will need to have special support measures in place."
Twyford said the Epsom MP was scaremongering by using such language in his invitation to residents.
He said one in six people in New Zealand had been diagnosed with a common mental disorder at some time in their lives, and it was irresponsible for an MP to stigmatise them.
"Anyone, from any community, can suffer from mental health issues. Whether you live in a 10-bedroom mansion or a state house is irrelevant."
National leader Simon Bridges said today that he would not have used Seymour's words.
"I think he's trying to make the point that there's a building there, there's issues there, but look, I wouldn't have said it."
Seymour was unrepentant, saying that it was more important to solve the problem than be "precious" about his language.
"Frankly, sometimes you need to tell it like it is. And the truth in this particular case is that people in this neighbourhood have been victimised by Housing New Zealand."
Constituents had raised various problems at the Banff Ave site and these would only get worse if the development was made five times bigger, he said.
"You look at the reports from the meeting - daytime public urination, abuse, women feeling intimidated and unsafe, in one case being grabbed while going for a run."
He and his constituents understood the need for housing supply to increase and that not all people could buy homes on the private market.
"None of that's controversial. The question is are you going to dump 25 dwellings worth of people into a location where they don't have proper support?
"Because if that's the case, the people are quite rightly concerned about the impact it might have on them."
Housing NZ was not required to notify the neighbourhood about its plans, and some residents complained at the meeting that they had been left out of the loop.
One of the residents at the meeting, Clare Turner, said she was concerned about the safety of children on the busy street.
"My daughter should be able to go to the BP down the road for icecream and not be afraid."