The Federal Trade Commission has granted early termination of the 30-day waiting period under the federal Hart-Scott-Rodino Antitrust Improvements Act with regard to the acquisition.
Expiration or termination of the waiting period is one of the conditions required for completion of the acquisition.
The transaction still requires approval by Piedmont shareholders and the North Carolina Utilities Commission.
Duke Energy and Piedmont also are providing information regarding the acquisition to the Public Service Commission of South Carolina and the Tennessee Regulatory Authority.
The companies are targeting a closing of the transaction by the end of 2016.