Labour says Paula Bennett should never have told her staff that Te Puea Marae chairman Hurimoana Dennis had revealed to her he was under police investigation.
Ms Bennett confirmed she briefed members of her staff on the meeting she had with Mr Dennis last Friday, and had told them about the investigation.
Phil Twyford says the information Mr Dennis gave Ms Bennett was confidential, and she should have kept it that way.
"It's completely unacceptable that Paula Bennett briefed her political staff on the police investigation into Hurimoana Dennis after her meeting with him, despite it having nothing to do with her social housing portfolio," Mr Twyford said.
"The information disclosed by Mr Dennis should have been kept confidential by the minister -- instead, the first thing she did was to brief staff members on the investigation.
"That's unethical and irresponsible."
One of Ms Bennett's press secretaries on Monday told a reporter about the investigation, which has led to calls for Ms Bennett's resignation.
She told Parliament on Wednesday she didn't know her staffer had spoken to a reporter until she was questioned about it on Tuesday.
Ms Bennett says her press secretary believed the police investigation was public knowledge, and had mentioned it in passing while she was talking to a reporter.
She denies opposition claims that it was a deliberate attempt to smear Mr Dennis, whose marae has opened its doors to homeless people.
The inquiry is reported to involve the way Mr Dennis intervened, on a personal basis and outside working hours, on behalf of a teenage boy who was in a sexual relationship with a 15-year-old girl.
Mr Dennis is reported to have helped arrange for the teenage boy to move to Australia.