Labour says the government is spending $140,000 a day putting up homeless families in motels.
Housing spokesman Phil Twyford bases the number on official figures, and says they show 30 times as many families need emergency housing in motels than the government had expected.
"National thought they would need to issue just 350 emergency housing grants for motels every three months - in the last three months they issued 11,446," he said.
"The cost has risen by two-thirds in just half a year, from $7.7 million in December to $12.6m in June.
"National had budgeted just $2m a year but are spending nearly $140,000 a day."
Mr Twyford says it's a legacy of "knocking down state houses" and under-estimating the scale of the problem.