The Labour Party wants an assurance that operational cuts won't lead to another incident where Child Youth and Family loses confidential files.
It emerged on Wednesday that documents were found in a car the agency was selling in Auckland.
Child Youth and Family says cars put up for auction are meant to be cleared first, and has apologised unreservedly.
The agency sells about 500 cars a year and has begun looking at its procedures to see how the files were left in the vehicle.
Labour's social policy spokesperson, Annette King, says nobody likes the thought of personal information being available to strangers.
She says the Social Development Minister, Paul Bennett, needs to promise there won't be a repeat because of cuts to what the Government describes as back-office functions.
Ms Bennett's office says the Minister will not comment because the incident was an operational issue.