Hostplus, which declined to respond to Mr Pape, denied that it was trying to restrict investors and said the changes were administrative.

Nonetheless, the fund's chief investment officer, Sam Sicilia, has criticised the decision to allow people who have lost their jobs to withdraw up to $20,000 from their accounts, tax free.

Early withdrawals are likely to hit Hostplus hard because many of its investors are hospitality staff who have become jobless, and its flagship balanced fund has a policy of not investing in cash-like securities. Without cash, the fund will be forced to sell assets, locking in losses.

To calm concerns about its liquidity, Hostplus two weeks ago disclosed it had $6 billion in cash. But Hostplus executives won't clarify if the balanced fund has access to the money.

Hostplus is one of the best-performing super funds over the short and long term, in part through its investments in ports, airport and tollroads, venture capital and private equity funds.

Mr Pape, a financial counsellor whose book has sold more than 1 million copies, said he didn't intend to leave Hostplus, but criticised investments in these assets, which can generate high management fees and aren't easy to value because they aren't traded on financial markets.

"If you read my stuff, you’ll see I’ve been warning people about the dangers of unlisted assets, and high fees for years," he said.

"You’ll see that I’ve mentioned many of them in my columns and books. Anyway, it’s for all these reasons that I’ve consistently advocated investing super in simple low-cost index funds, like Warren Buffett himself recommends."

On a recent Facebook survey conducted by Mr Pape, more about 90 per cent of 64,600 people said they wouldn't withdraw money from their superannuation.

Clarification: An early version of this article referred to Mr Pape as a financial adviser, instead of a financial counsellor.