The SEC slammed Citigroup Global Markets with a $7 million penalty for providing the agency with incomplete trading data, the largest penalty for so-called "blue sheet" violations to date.

Citigroup admitted to wrongdoing, saying the deficient trading data was due to a coding error in the software it used from May 1999 to April 2014. As a result, almost 27,000 securities transactions were omitted from Citigroup's responses to more than 2,300 blue sheet requests.

Image: Bloomberg
Image: Bloomberg

After discovering the coding error, Citigroup failed to report the incident to the SEC or take any steps to produce the omitted data until nine months later, the SEC said.

"Broker-dealers have a core responsibility to promptly provide the SEC with accurate and complete trading data for us to analyze during enforcement investigations," Robert Cohen, co-chief for the SEC Enforcement Division's Market Abuse Unit, said in a statement. "Citigroup did not live up to that responsibility for an inexcusably long period of time."

The SEC collects blue sheet trading data such as time of trades, types of trades, volume traded, prices and other customer identifying information.

Danielle Romero-Apsilos, a spokeswoman for Citigroup Global Markets, said the firm was pleased to have resolved the matter.