Agency officials say the technology -- called "carbon capture and storage" -- is ready now for commercial applications to reduce carbon emissions from electrical power generating plants fueled by coal.
But energy experts say the regulation, part of the New Source Performance Standards released Jan. 8, means no new coal plants can be built because the technology is a long way from ready for commercial use.
The emails were first made public Jan. 10 by the Washington Free Beacon, and include an August 2012 message from the Sierra Club's John Coequyt, head of the group's "Beyond Coal" campaign, to EPA officials Michael Goo and Alex Barron.
The email included a copy of a news story with the headline, "Coal to remain viable, says EPA's McCarthy at COAL-GEN keynote."
"Pants on fire," Coequyt said of the headline to Goo and Barron.
"What they're doing is they're not being straight with the public, they're not being straight with the Congress, they're not being straight with everything, and I think that's what these emails show," said Dan Kish, vice president for policy at the Institute for Energy Research.
"This is an inside joke. I mean, would you ever use that in an email to someone you weren't an intimate with? It's like a red flag to me," Kish said.
"It's an inside joke that has vast ramifications for this country," he said, because 40 percent of the nation's electrical power is generated by coal-fired plants.
The emails, which were obtained by transparency activist Christopher Horner through a Freedom of Information Act request, document a series of meetings, calls and written exchanges between EPA and the Sierra Club about the emissions standards and how they would affect new coal plants.
The Sierra Club's "Beyond Coal" campaign aims to replace the majority of coal plants with alternative energy sources.
In one exchange, Coequyt worried that if the EPA set achievable standards for new plants, facilities now on hold would be built.
"Attached is a list of plants that the companies said were shelved because of uncertainty around [the] regulations. If a standard is set that these plants could meet, there is not a small chance that the company could decide to revive the proposal," Ceoquyt told Goo and Barron in April 2011.
In September 2011, Coequyt told Barron the Sierra Club was "very worried" that as many as 20 new coal plants in the permitting process would be built.
Coequyt also suggested locations for public hearings on the rule in 2012, naming places Jim Martin, then EPA Region 8 administrator, said in another email would be friendly toward the proposed regulation.
"As the email productions in this litigation make inescapable, Sierra Club (in particular) has the ear of senior EPA officials," said Horner, who is director of litigation at the American Tradition Institute.
"They feel it is appropriate — and fruitful — to argue, for example, that EPA must ensure its [greenhouse gas] standard is set sufficiently high to keep Sierra's priority list of coal plants off-line.
"They play matchmaker for agency and Sierra — and other group — staff. And otherwise behave as if they see no distinction between the entities but a trifling constitutional impediment to be disregarded as often as possible," Horner said.