Harvard University law professor Laurence Tribe was once a mentor to Obama at Harvard Law School, calling him “the best student I ever had and the most exciting research assistant.”

However, he is less than impressed with the administration’s carbon rule for power plants, saying that it is “a remarkable example of executive overreach” and raises “serious constitutional questions.”

Hope his tax paperwork is in order!

Tribe, who submitted joint comments to the Environmental Protection Agency with coal producer Peabody Energy Corp. (BTU), 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“The Proposed Rule lacks any legal basis and should be withdrawn,” Tribe and Peabody wrote in their filing, which law firms for the company said was submitted to EPA on the Dec. 1 deadline.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 e-mail 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.

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.

…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.”