This is also the second class action filed against AMP this year, with Maurice Blackburn announcing it had filed a class action against the financial services group last month on behalf of superannuation holders.

The case alleges that, through arrangements entered into with related parties, trustees AMP Super and NM Super paid too much to related AMP entities for administration services.

It also alleges they failed to secure an appropriate return on cash-only investment options.

Slater & Gordon senior associate Nathan Rapoport said superannuation members trusted that AMP would act in their best interests when managing their retirement savings. Instead, they charged exorbitant fees, he said.

“Both AMP Super and NM Super, as trustees of the funds, should have taken steps to secure the best deal for members on a commercial arms-length basis,” Mr Rapport said.

“Members whose funds were deposited in cash-only investment options were short-changed potentially thousands of dollars because they received interest rates below what a reasonable and diligent trustee could have obtained on the open market.”

The law firm said that the royal commission heard evidence of a particular group of AMP cash option members who received negative returns due to a combination of an un-competitive interest rate and excessive fees, and the trustee was not even aware of this.

“These customers would have been better off keeping their retirement savings under their bed,” Mr Rapoport said.

The case claims compensation for this conduct dating as far back as 1 July 2008.

In a public statement, AMP said it would vigorously defend the class action proceeding filed by Slater and Gordon.

“AMP and the trustees of its superannuation funds are firmly committed to acting in the best interests of their superannuation members and acting in accordance with legal and regulatory obligations. We encourage any customers who have concerns to contact AMP,” AMP stated.

“We have reduced the administration fees on some of our cash investment options to address the issue of negative returns in the small number of funds impacted by this issue. We are also compensating affected customers for lost earnings.”

AMP also noted that in 2018, it cut fees on its flagship MySuper products which benefitted approximately 600,000 existing customers as well as new customers. In 2019, it also cut fees to MyNorth.