What happened to John Cunningham’s Stock in Sierra Mills?

John Cunningham's stock in Sierra Mills is stolen and stricken from the books. He is unable to prove that he has any stock in the company.
When the time comes for Cunningham to get the dividends from his stock in Sierra Mills, the money does not arrive. When he writes to the secretary of Sierra Mills to inquire about why the quarterly dividends didn't appear, she says that there's no record of Cunningham owning any Sierra Mills stock.
Cunningham goes to the bank and finds that his safe deposit box is empty; there are no Sierra Mills stock certificates. The Iron Heel took them in order to bankrupt Cunningham and remove any influence he has. It is likely that this stems from his allegiance to socialism, which the Iron Heel wants to stamp out. 
Cunningham takes Sierra Mills to court, but cannot prove that he ever owned stock. As London writes, "He did not control the courts, and the Sierra Mills did."
Eventually, a fake mortgage is foreclosed on and Cunningham loses his home as well.