Moody’s Investors Service Inc. placed the credit rating of Sempra Energy (NYSE: SRE) on review for a downgrade, announcing its decision June 25. Moody’s said it did not expect the review to result in more than a one-notch downgrade. The decision affects approximately $12 billion in debt securities.

Among the concerns cited by a Moody’s analyst was increased leverage to fund Sempra’s acquisition of its majority stake in Oncor Electric Delivery Co. LLC, a Texas utility. Sempra, which took on an 80.25 percent stake in the utility for $9.45 billion, wrapped up its acquisition in March.

Moody’s said it was also concerned about the recent overture from activist investors Elliott Management and Bluescape Resources, specifically that it “heightens the execution risk associated with any initiatives that Sempra may undertake in order to improve its credit quality.”

Other concerns listed by Moody’s were delays in the construction of the Cameron liquefied natural gas project in Louisiana, and the California regulatory environment. In April, Moody’s downgraded the rating outlook of Sempra subsidiary San Diego Gas & Electric Co. because of the latter, citing concerns about “electric utilities’ exposure to strict liability under inverse condemnation relative to wildfires.”

Moody’s gives Sempra a credit rating of Baa1. With a single-notch downgrade to Baa2, Sempra’s debt would still be considered investment grade, carrying moderate risk. Ratings must fall two more pegs on the Moody’s scale to be considered speculative.

“Maintaining strong investment-grade credit ratings is important to us and we are pleased that Moody’s is recognizing our efforts to de-risk our portfolio,” Sempra spokesman Doug Kline said. “We look forward to communicating with them and all stakeholders on our various initiatives.”

Kline also said that Sempra sees positive things ahead with the Oncor buy: “With Oncor — a strategic and transformational acquisition — we have more opportunities to accelerate earnings growth over the long term and reposition our asset portfolio to help strengthen our balance sheet.”

UPDATE: This post has been updated with more details about the Moody’s rating system.