It is estimated that one in three Australians could benefit from a record class action lawsuit against Australia's largest banks.
The lawsuit, which is being launched by the law firm Slater and Gordon on Tuesday, is on behalf of Australians whose super is invested in cash at banks.
Up to five million people have some type of cash super cash with retail funds owned by banks, and it is considered a safer option, especially among older Australians.
Up to five million people have some type of super cash with retail funds owned by larger banks (pictured), which is seen as a safer option, especially for many older Australians.
The law firm alleges that the bank-owned superfunds are putting members' money in their parent bank instead of the bank that offers the best interest rate.
As a result, members are paid between 0.5 and 1 percent less interest than they would normally receive, leaving them out of pocket, news.com.au reported.
The head of collective actions of Slater and Gordon, Ben Hardwick, told the publication that low interest rates and excessive fees could hurt many Australian retirees.
"Slater and Gordon do not believe that this is fair and we are saying that it is enough," he said.
Hardwick said the first lawsuit will be against Colonial First State, owned by the Commonwealth Bank, as well as against AMP, with approximately 18 additional cases to follow.
"What funds like Colonial First State have been doing is pulling super with a parent bank like CBA.
"The interest of the parent bank is so low that investors in the cash option are receiving rates as low as 1.25 percent per year, which is even below the RBA's cash rate.
The first lawsuit will be against Colonial First State, owned by Commonwealth Bank, as well as against AMP, with approximately 18 additional cases to follow
As Mr. Hardwick explained, some industry and retail superfunds are paying members interest similar to standard term deposits: between 2.0 and 2.5 percent.
It is estimated that approximately 55 percent (or 8.2 million) of Australians have at least one retail account with some cash component.
While it is difficult to calculate the exact payment figure, the law firm estimates that for someone with $ 100,000 in cash at 0.5 percent for six years the payment is $ 3000.
The law firm has created the getyoursuperback.com website for anyone whose super is invested in cash.
Daily Mail Australia has contacted the Association of Banks of Australia to get their comments.