Harvard University law professor Laurence Tribe, a mentor to President Barack Obama, said the administration's carbon rule for power plants is "a remarkable example of executive overreach" that raises "serious constitutional questions."

Tribe, who submitted joint comments to the Environmental Protection Agency with coal producer Peabody Energy Corp., said the agency should withdraw its plan to cut emissions from power plants because it reverses decades of federal support for coal.

"The Proposed Rule lacks any legal basis and should be withdrawn," Tribe and Peabody wrote in their filing, which law firms for the company said was submitted to EPA on the Dec. 1 deadline. Peabody, the nation's largest coal producer, has declined more than 44 percent in trading since the EPA plan was unveiled at the beginning of June.

Calls and email messages left with Tribe's assistant at Harvard weren't immediately returned. Lawyers at two law firms listed on the filing confirmed that Tribe's comments were genuine.

Replacing coal

The EPA's plan is the centerpiece of Obama's effort to combat global warming. The proposal would require a 30 percent cut in carbon emissions by 2030 from 2005 levels. The plan is designed to replace coal as the chief source for electricity generation with natural gas, renewable power and efficiency.

The EPA said it is combing through more than 1.6 million comments it has received on its proposed rule, which is set to be finalized next June.

The agency responded Friday, saying Supreme Court decisions have given it the authority to regulate greenhouse gases, which are blamed for causing global warming.

"History has shown us that EPA writes solid rules and they stand up in court," Liz Purchia, an agency spokeswoman, said in an email. "Courts have reaffirmed our science and reasoning time and time again.

"The Supreme Court made clear in 2007 and affirmed recently that EPA has an obligation to limit carbon pollution because it's a harm to human health," she said.

'Radical shift in policy'

Tribe, who has called Obama his most impressive student at Harvard Law School, raised a series of criticisms of the EPA's power rule, calling it "an extravagant and impermissible overreach by the agency."

•First, it "repudiates a policy of prudent use of coal" that dates back to the administration of President John F. Kennedy in the early 1960s, according to the filing.

•Second, the EPA plan violates the Fifth Amendment, because it takes private property without due process. "The Proposed Rule represents a radical shift in federal policy that upsets settled, investment-backed expectations," the company and Tribe wrote in their 36-page submission. The EPA is "forcing the United States' power plants and energy industry to bear the global burden of lessening carbon dioxide emissions."

•Third, contradictory provisions in the amendments of the Clean Air Act mean that the section being used by the agency to establish these rules "ignores basic principles of statutory construction" and raises separation of powers issues.

"At bottom, the Proposed Rule hides political choices and frustrates accountability. It forces states to adopt policies that will raise energy costs and prove deeply unpopular, while cloaking those policies in the garb of state 'choice' � even though in fact the polices are compelled by EPA," the filing concluded.

Tribe has taught at Harvard since 1968, argued 35 cases at the Supreme Court and authored 115 articles or books.

In 2010 Obama appointed him senior counselor for access to justice at the Justice Department. Tribe also argued a Supreme Court case on behalf of former Vice President Al Gore in the disputed 2000 presidential election.