Judith Collins has accused the Government of being "miserable" for taking away tax cuts National legislated for before the election.
Under the cancelled cuts, a person earning $52,000 a year was in line for $20 a week extra in their back pocket. Labour promised to can that if it formed the new Government.
"It's your Government that's going to get rid of the $1000 extra that every family was going to be getting under our Government," Ms Collins told Housing Minister Phil Twyford on The AM Show on Friday morning.
"You're just miserable."
It comes a day after a report showed a reduction in child poverty. Twelve percent of children are living in material hardship now according to the Child Poverty Monitor, down from 14 percent in the previous report.
The Prime Minister has made herself Child Poverty Minister, and Mr Twyford said the Government will soon "legislate a clear set of targets and measurements for child poverty that the past Government constantly refused to".
He rejected Ms Collins' claim the Government's cancellation of the tax cuts would stop more children being lifted out of material hardship.
"Your tax cuts actually put more than $400 million into the top 10 percent of earners," he told the former Police Minister.
"Our package, which we're going to release next week, will do far more to relieve child poverty than anything your Government does."
During the election campaign, National repeatedly accused Labour of planning to raise income tax. Newshub political editor Patrick Gower called it "the biggest" lie of the campaign.