U.S. regulators on Friday charged a money manager made famous by Michael Lewis’s book “The Big Short” with misleading investors on a complex structured product in 2006.

The Securities and Exchange Commission accused the New Jersey firm Harding Advisory and its owner, Wing F. Chau, of fraud, alleging that they allowed a hedge fund to control which assets backed a $1.5 billion complex structured product, without disclosing to investors the fund’s role in the process.

Chau appeared in Lewis’s bestseller about the financial crisis and later sued the author for defamation but lost.

According to the SEC, Harding and Chau compromised their independent judgment as collateral manager for a collateralized debt obligation known as “Octans I CDO Ltd.”

A lawyer for Harding and Chau could not immediately be reached for comment.

The SEC did not charge the hedge fund, Magnetar Capital, which the agency said was allowed to select and acquire a portfolio of subprime mortgage-backed assets to serve as collateral for the debt issued to investors in the CDO.

According to a complaint filed in the SEC’s administrative court, Magnetar’s role in helping to select the assets for Octans I was “unbeknownst to investors and in conflict with marketing materials.”

Magnetar’s name has repeatedly surfaced in connection with risky bonds sold as the housing market began to collapse. Multiple regulators have said the firm helped structure certain deals and bet against them even though its role was not disclosed.

A year ago, Massachusetts’ top securities regulator forced State Street to pay $5 million for failing to tell investors about the role Magnetar played in creating CDOs. Magnetar has not been charged in any of the financial-crisis-era cases.

Magnetar spokeswoman Melinda McMullen declined to comment.

The CDO at issue in the Chau case failed in April 2008 and left investors with $1.1 billion in losses, the SEC said.