Inland Revenue's cracking down on unpaid tax bills.
It's been allocated an extra $35 million in Budget 25 to boost its tax compliance and collection activities.
The tax department expects to return an additional $4 for every dollar in the first year, and $8 in year two.
IRD Commissioner Peter Mersi told Mike Hosking it's hard to estimate how much tax is owed across the board.
He says they don't really know the size of the gap, but believes it's around $9 billion.
LISTEN ABOVE

Mike's Minute: How do you not have confidence in an event already sorted?
02:27

Pollies: National's Mark Mitchell and Labour's Ginny Andersen talk the handling of the fuel crisis and cost of living
11:20

John Edminstin: Bluff Oyster Festival Chair on low ticket sales, the chance this will be the final year
02:43