Federal regulators Tuesday fined the Chicago Board Options Exchange $6 million, saying its staff interfered with its three-year investigation of short selling at a member firm in an unprecedented breakdown of trading supervision.

The settlement, which calls for immediate remedial actions, is the first ever assessed by the Securities and Exchange Commission for violations related to regulatory oversight, according to a statement. Four days ago, an administrative law judge ruled that CBOE member OptionsXpress Inc., a unit of Charles Schwab Corp., helped facilitate sham transactions that violated U.S. securities laws known as Regulation SHO.

While actions against traders and investors are common at the SEC, exchanges enjoy legal protections in their capacity of self-regulatory organizations (SRO). In the CBOE's case, oversight suffered when it transferred responsibility for Regulation SHO enforcement from one department to another in 2008, the SEC wrote.