The New York Times is reporting (here) that the Obama Administration is preparing to regulate greenhouse gas (GHG) emissions from existing power plants for the first time. As a matter of policy, this step makes sense as existing electric power plants are the single largest source of carbon dioxide emissions in the US and worldwide.
As the story notes, this would be the most costly and politically contentious regulatory step the Obama Administration has yet taken on climate chnage; it would impact primarily on coal-fired power plants and everyone who gets electricity from those plants. Depending on how the regulations are structure, their main effect could be to cause coal-fired power plants to retrofit co-generation technologies, which would enable them to substitute natural gas, which currently is less expensive than coal and which is on net a less troublesome GHG (methane is a more potent GHG than carbon dioxide but resides in the atmosphere less than 1/10th as long).
Normally, it takes EPA 1-2 years to promulgate a major new rule on a contentious issue such as this. But I wouldn't be surprised to learn that staff at EPA have been working on the rudiments for a new existing source rule for some time already.