MLC has started a review process of denied disputed claims practices with a focus on critical illness, including heart attacks.
In a statement, MLC said the review process of denied claims will go back as far as 1 January 2014.
NAB Wealth's group executive Andrew Hagger said this was the "right thing to do" to provide certainty to the bank's customers.
"We are confident that we have the right claims processes in place. Providing contemporary life insurance cover to our customers with a claims process that is as simple and empathetic as possible is our priority," Mr Hagger said.
"However, we believe it is the right thing for leading insurers to do to provide customers and advisers certainty about their claims processes."
He added: "That's why we have announced that we will start a process to review denied disputed claims practices over the last two years, with a particular focus on critical illness, including heart attacks."
As part of the review, MLC will be working with independent customer advocate Dimity Kingsford Smith on the implementation of the review process to ensure that the interests of "customers are at the centre" of its work.
"We believe our claims processes are industry leading. We consciously employ health professionals like doctors, nurses, physiotherapists and psychologists in our client-facing claims teams to improve the customer claims experience, pay claims and help customers return to work," Mr Hagger said.
"And, over recent years, we have continuously improved our claims processes – including reducing the case load in our claims teams by around 30 per cent so our people can help customers more. We want customers to spend more time focusing on getting well, and less time filling in forms for us."