Gina Rinehart changed the constitution of her family's mining company, Hancock Prospecting, so her children would lose their shares to her if she was removed as head of the family's multibillion-dollar trust, a court has heard.

In the latest revelation to come from the continuing court battle between Australia's richest person and two of her children over control of the Hope Margaret Hancock Trust, the NSW Supreme Court heard on Tuesday that Mrs Rinehart allegedly used her controlling stake in Hancock Prospecting to put a ''poisoned pill'' into its constitution in March 2006.

Changed the constitution of Hancock Prospecting: Gina Rinehart.

The two dissenting children - John Hancock and Bianca Rinehart - claim this took the form of an amendment stating that if Mrs Rinehart were replaced as the head of the family trust by anyone other than another member of the Rinehart/Hancock family, the remaining shares in the company that were held by the trust would immediately be put up for sale.

The pair want Mrs Rinehart replaced by an ''independent trustee''.