Duke Energy Corp. (DUK) and Progress Energy Inc. (PGN) said Monday that a new decision by federal regulators on their merger would enable the companies to close their merger by July 1.

The Federal Energy Regulatory Commission approved the merger, assuming the companies meet certain conditions, in a decision released late Friday.

Duke Energy's $26 billion all-stock deal for Progress was disclosed in January 2011 and would create the nation's largest utility.

The FERC issued a similar type of decision last year, saying "yes" to the merger, but requiring a set of conditions that would ensure the combined company wouldn't exercise undue influence over the power markets in the Carolinas. Afterwards, the commission rejected two market-mitigation plans the companies filed.

The companies need to be able to meet the conditions of the FERC decision and get the approval of regulators in North Carolina and South Carolina.

"We are pleased that the FERC has conditionally approved the merger, our Joint Dispatch Agreement and Joint Open Access Transmission Tariff," Jim Rogers, Duke's chairman, president and chief executive said in a statement. "We will quickly complete the evaluation of the conditions in the orders while working to obtain the remaining regulatory approvals to close the merger on July 1."

Shares of Duke were up 0.4%, at $23.16.

Duke and Progress said they would file documents that the FERC requested to comply with the decision in the next 15 days. The FERC gave the companies 60 days in which to explain how they will implement the required changes.

Among several conditions, the FERC prohibited the companies from selling their most-expensive energy only to new customers, while reserving their less-expensive energy for existing customers. The FERC also directed the companies to explain in more detail how the two companies will share in cost savings from jointly owning their facilities.

Duke, which serves customers in the Carolinas, Indiana, Ohio and Kentucky, also operates wholesale power and renewable-energy business and has international operations in Brazil and elsewhere.