The Transport Agency is collecting tens of thousands of dollars in unpaid tolls from Auckland's Northern Gateway.
The 7km road between Orewa and Puhoi has been open for 10 months and is New Zealand's first fully electronic toll road.
After the first five months of operation, about 28,000 drivers owed more than $200,000 in unpaid tolls.
In the past month, the Transport Agency has clamped down and sent debt collectors to pursue larger amounts.
The agency's Auckland and Northland director, Wayne McDonald, says seven people had a toll debt of $300 or more.
Mr McDonald says compliance for paying tolls is expected to increase over time from the current figure of 94%.