The U.S. Securities and Exchange Commission may issue an enforcement action against S&P Dow Jones Indices LLC, a joint venture between leading financial data provider S&P Global Inc. and exchange giant CME Group Inc.

In the second quarter, the index provider received a Wells Notice from the SEC stating that the regulator's staff had made a preliminary recommendation to file an enforcement action against Indices over inadequate disclosures of a quality assurance mechanism and the mechanism's impact on certain volatility-related index values that were published on one specific trading day in 2018.

S&P, which is the parent company of S&P Global Market Intelligence, S&P Global Ratings and S&P Global Platts as well as Indices, disclosed the notice in a quarterly filing released July 28. It did not disclose the exact date that is in question in the Wells Notice.

A Wells Notice is a letter from regulators that alerts a company of potential action it is considering taking and allows it to provide a response before any official enforcement proceeding is taken. S&P said the notice is "neither a formal allegation nor a finding of wrongdoing." Indices "has been cooperating with the SEC in this matter and intends to continue to do so," S&P said in its filing. The SEC's recommendation could lead to "a civil injunctive action, a cease-and-desist proceeding, disgorgement, pre-judgment interest and civil monetary penalties," according to the filing.

In a statement, a spokesperson for S&P Dow Jones Indices said the index provider "has established rigorous processes to maintain the transparency and integrity of our benchmark determination process, and protect the independent governance and quality of our indices."

CME, one of the largest financial exchange operators in the world, has been aware of the notice, CFO John Pietrowicz said on the company's earnings call July 29. Pietrowicz added that the notice "is something that does not impact our trading business at all" and referred questions from analysts about it to S&P. A spokesperson for the Chicago-based exchange operator said CME had no further comment.

The SEC declined to comment on the Wells Notice.