The Commerce Commission says its ongoing consumer credit dispute with Motor Trade Finance is its most significant case for establishing rules on what fees lenders can charge.
Mark Berry, chairman of the anti-trust regulator, told the commission's annual conference this week that consumer credit remains a priority area.
It will use the courts to clarify the boundaries after recent changes to the Credit Contracts and Consumer Finance Act 2003, which came into full effect this month.
The commission is in a legal battle with the car finance business and Sportzone Motorcycles over alleged breaches of the CCCF Act and the Fair Trading Act.
"The consumer area has been one where there has been a particular uplift in work, following legislative amendments in recent times," Berry told the Competition Matters 2015 conference in Wellington.