The transactions between Dallas-based CLST Holdings Inc. and Fair were the subject of an IBJ article early this year that raised questions about conflicts of interest.

Publicly traded CLST revealed the SEC investigation in a filing with the commission. The filing said that the company, Durham, CEO Robert Kaiser and director David Tornek all received subpoenas.

The filing reveals for the first time that the SEC is conducting its own investigation of Durham's business dealings and that the probe extends beyond Fair Finance, the consumer-finance firm Durham co-owns. The only previously public federal investigation was one being conducted by the U.S. Department of Justice.

Read More: SEC probing Durham deal with Texas firm