National's under pressure to come clean on what new taxes it could be considering.
The party's unveiled its budget responsibility rules, promising to deliver a surplus and rein in spending.
But finance spokeswoman Nicola Willis has only ruled out higher taxes on working people, leaving the door open to other tax increases.
Former Finance Minister Steve Joyce told Mike Hosking that bed and fuel taxes are the most likely options.
LISTEN ABOVE

Mark the Week: Luxon stared them down again
02:39

Mike's Minute: It's not the taxpayers' job to "clean up" businesses
02:20

Wrapping the Week with Kate Hawkesby and Tim Wilson: The National leadership challenge, the party for 100 Years of ZB
10:14