Gina Rinehart's private iron ore mining company Hancock Prospecting has failed in its bid to keep its financial reports secret.
The Australian Securities and Investments Commission (ASIC) said Hancock and its related entities had in late 2011 applied for relief from having to lodge financial reports, including company accounts, for a range of periods.
Such disclosure is required under Chapter 2M of the Corporations Act.
But the corporate watchdog on Thursday revealed it had knocked back the request.
"ASIC declined these relief applications on 2 March 2012," ASIC said in a brief statement.
But Ms Rinehart's companies are fighting ASIC's decision and have taken their case to the Administrative Appeals Tribunal for review.
CMC Markets chief market strategist Michael McCarthy said Hancock's application seemed like a long shot.
"In broad terms, it does seem a little extraordinary: private or not, you still have to pay tax, for example," Mr McCarthy told AAP.
"It would be natural that most Australians would expect some form of regulatory oversight, especially for such a large company.
"It's in the category of `you can't blame someone for trying but don't be surprised if the answer is no'."
Exemptions from the requirement to lodge financial reports are rarely granted.
In most cases, relief is not granted for financial reports that were due in the past.
However exemptions can be granted for foreign-controlled companies with parent entities registered with ASIC and which lodge consolidated financial reports in offshore markets that include Australian arm's activities.
"Generally, it is the minority of cases that qualify for some form of relief," the corporate watchdog said on its website.
Companies are generally required to lodge reports with ASIC when substantial sums of money are involved, the general public has invested funds with the firm, or the company was a charity and was not intended to make a profit.
In Hancock's case, large sums of money are most certainly involved, with its iron ore mines costing several billion dollars each to develop.
Ms Rinehart, the highest ranking Australian on the Forbes Rich List at number 29, is currently battling on several fronts to keep her affairs under lock and key.
Her court battle with her three eldest children over control of the multi-billion dollar family trust continues, along with an associated case against Kerry Stokes-chaired Seven West Media and Steve Pennells, a senior reporter for the publisher's newspaper The West Australian.
She is trying to force the newspaper to hand over documents and recordings that could expose the sources behind a series of articles Pennells wrote about the family feud.
Separately, her estranged son John Hancock is poised to head a company that makes wall panels that could take a slice of the brick market, according to a report in The Australian Financial Review.
The product could reduce the amount of steel used in construction - an irony given Ms Rinehart's $17 billion personal wealth has mainly come from iron ore exports.