Environmentalists are urging Maryland regulators to reverse a decision to allow utility giant Exelon to buy state power companies Pepco and Delmarva Power, arguing that the merger threatens to kill off renewable energy development and raise costs for consumers.

A coalition of environmental groups announced Monday that they filed for a rehearing with the Maryland Public Service Commission, which approved the Exelon merger in May, according to lawyers with the group Earthjustice.

"There are significant and real risks that Exelon will use this merger to increase energy bills over the next few years to subsidize its failing investments in nuclear power," said Susan Stevens Miller, Earthjustice's lead counsel in the case.

The merger was approved in a 3-2 decision. The environmental groups argue that the majority decision "is flawed" because it failed to consider "the harm to Maryland and ignored statutory directives."

The groups say the merger would complete Exelon's acquisition of regional utilities, giving it control of electricity delivery to nearly 2 million residents in Maryland.

"The minimal additional conditions imposed by the commission will not offset the harms caused by this merger. Exelon's long history of hostility to renewable energy and competition from small clean energy businesses is a threat to the future of homegrown clean energy projects in Maryland," Miller said.

Activists say Exelon's campaign against federal wind energy subsidies presents a challenge for the state to meet its renewable energy and efficiency goals if the merger is approved. There is also concern the utility will use revenue from the multi-billion dollar merger to support its aging fleet of nuclear power plants.

Exelon says it is the nation's 11th largest wind developer.

The nation's largest nuclear energy utility, Exelon also has argued that the federal Production Tax Credit for wind energy is a market-distorting policy, which is making it more difficult for its power plants to remain economically competitive.

The utility argues that the wind credit hurts pricing in the electric markets where it operates, which sets the price of electricity at a rate at which nuclear plants and other non-renewable energy cannot economically sustain operations.

Earthjustice filed the appeal on behalf of the Sierra Club and the Chesapeake Climate Action Network