There are concerns a lack of knowledge among Inland Revenue staff is costing the country millions of dollars.
The number people worth more than $50 million has increased 75 percent in the past five years to 350 people.
But despite more super-rich earners, the amount of disputed tax has decreased from $112 million to just over $85 million in the same period.
Tax consultant Terry Baucher told Kate Hawkesby he's concerned the level of expertise is nowhere near what it used to be.
"Very highly experienced people have left. They are the people who have the institutional knowledge, know the ins and outs of tax law, and have the skills to take on the high wealth individuals."