Three private companies owned by iron ore magnate Gina Rinehart have pleaded guilty to failing to submit financial reports on time.

Hancock Prospecting, Hancock Minerals and Hope Downs Iron Ore were pursued by the Australian Securities and Investments Commission (ASIC) for late lodgement of annual records during a five-year period from 2008.

Lawyers representing the companies told the Perth Magistrates Court of concerns that the information contained in the financial statements could be used by larger firms in commercial negotiations.

The companies are facing 13 charges relating to breaches of the Corporations Act during the 2008 to 2012 financial years.

Private companies are required by law to file annual reports within four months of June 30, the end of the financial year.

One annual report was submitted by Hancock Prospecting 785 days after the deadline had passed.

The company's lawyer, Mr Neil Williams SC, told the court it had been contesting whether accounts needed to be lodged at all during the period in question.

He said the companies would not have breached their financial obligations in that time if ASIC had suspended its requirements until the matter was resolved.

While a guilty plea was put forward by the companies, the court was unable to accept it because the plea was not in writing.

The case was adjourned until next Monday.