Environmental groups are trying to block changes to the Genesee 3 power plant southwest of Edmonton.

When construction of the coal-fired plant was approved, the company volunteered to offset slightly more than half of its greenhouse gas emissions. Coal generators emit more carbon dioxide than any other kind of power plant, but the offsets would have brought Genesee 3 in line with the emissions of a typical natural-gas plant.

Ontario's Atikokan power station, like the Genesee units southwest of Edmonton, runs on coal, which emits more carbon dioxide per megawatt of electricity than any other fuel.

Now, however, Capital Power is asking Alberta Environment to amend the approval, arguing that the economics have changed and it can't competitively afford the costs of carbon offsets.

If successful, the plant would only have to abide by greenhouse gas laws implemented in 2007, meaning it would be on the hook for a much lower reduction.

Chris Severson-Baker, national policy director of the energy think-tank Pembina Institute, said Alberta Environment should reject the changes. If the plant's operating conditions were changed, it would have effects far beyond the Genesee 3 facility, he said.

"It would undermine the process that we have in Alberta that has worked out quite well in a number of cases," Severson-Baker said. "It would weaken the process, and it would remove some of the faith that people have in the reducing-emissions offsets.

"They need to reduce according to both the approval agreement and the province's 2007 rules."

A group called the Clean Energy Coalition, which includes the Pembina Institute and landowners near the Genesee plant, has written to Alberta Environment to urge it to hold Capital Power to its original promise.

"Corporations who make public commitments to induce approvals ought to be held to those commitments," the letter says.

Alberta Environment and the Alberta Utilities Commission are both considering Capital Power's request.