ASB currently wants customers to go direct with any applications, rather than through their broker.
The stance has angered advisers, who say they have been "frozen out" by the bank during the Covid-19 crisis.
A spokeswoman said: "ASB is currently asking its customers to apply directly to the bank to apply for mortgage relief, and is now reviewing this process."
Grant Gilbert, ASB's general manager for specialist lending & business development, said customers should take advice from their broker before they make changes to their mortgage.
“It’s really important that customers understand the long-term implications of mortgage deferral or interest only arrangements, and we encourage customers to talk to their broker about the best solution for them.
"We established the online application process to make it quick and easy for our customers to apply for the assistance they need. Based on feedback from customers and brokers we are currently reviewing our process.”
ASB will provide a further update later this week. The bank is expected to adopt a policy in line with the other big four banks, which allow advisers to make applications on behalf of their clients.