Duke Energy and Progress Energy asked a federal agency Friday to reconsider its rejection of a plan to address competition concerns over their proposed merger.

Duke spokesman Tom Williams said the filing was a formality to preserve the utilities' rights before the Federal Energy Regulatory Commission. They had 30 days, ending Friday, to appeal the commission's Dec. 14 order.

The commission concluded in September that the merger would reduce competition for wholesale power in the utilities' home turf of the Carolinas. Last month, FERC also rejected the utilities' plan to solve that problem, ruining their goal of closing the merger by the end of 2011.

Duke and Progress intend to file a revised plan but don't have a firm schedule by which to file it, Williams said. The revised plan must be filed with the N.C. Utilities Commission before it is submitted to FERC.

Duke and Progress had offered to answer the competition problem by offering short-term contracts for wholesale power in the Carolinas.

The commission, in its rejection last month, said there's no evidence such an offer would attract buyers. Nor would the proposal force Duke and Progress to give up control of the energy they offered for sale, it said.

Friday's rehearing request outlines where Duke and Progress believe FERC was wrong.

It asserts that FERC failed to consider key elements of the utilities' mitigation plan. Among those factors, it says, were the limited wholesale markets in their Carolinas territory and the nature of the electricity sales Duke and Progress would offer.

"Consequently," the filing read, "the commission erroneously concluded that the applicants' proposal would not mitigate the market power identified in the merger order when, in fact, that proposal was tailored to address the exact concerns that the commission had raised."