"The bottom line is this leads to delays for coal plants," David Bookbinder, a lawyer for environmental group the Sierra Club.
Delays could be bad news for the industry especially as the United States may soon regulate greenhouse gases as President-elect Barack Obama has promised to do, he added.
A section of the EPA ruling said, "The Board recognizes that this is an issue of national scope that has implications far beyond this individual permitting proceeding."
Environmentalists said the wording opens up the EPA to reconsidering permits in other states.
In a landmark ruling in 2007, the Supreme Court found that carbon dioxide can be regulated as a pollutant under the U.S. Clean Air Act.
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