The Trump administration will put forward this argument to allege the Clean Power Plan violates the law, Bloomberg News reported.
"The Clean Power Plan departed from this practice by instead setting carbon dioxide emission guidelines for existing power plants that can only realistically be effected [sic] by measures that cannot be employed to, for, or at a particular source," Bloomberg quoted from the unreleased documents.
Politico, The New York Times and The Washington Post also reported aspects of the plan, citing unreleased documents. The EPA declined CNBC's request to comment on the reports.
Some experts say weakening the Clean Power Plan will not change the fortunes of the coal industry, which has lost significant share of U.S. power generation to cheap, abundant U.S. natural gas.
"Pruitt claims 'the war on coal is over.' But the so-called 'war on coal' is less a regulatory action than a function of markets," said Thad Lightfoot, who previously worked as a trial attorney with the U.S. Justice Department's environment division and a legislative aide to Democratic former House Speaker Thomas Foley.
"Even with the Clean Power Plan under a Supreme Court stay and the subject of litigation, utilities — particularly large investor-owned utilities — are retiring older, inefficient coal-fired plants because they are too costly to retrofit," added Lightfoot, now a partner at law firm Dorsey & Whitney.
The documents do not explicitly indicate that the EPA will replace the Clean Power Plan.
The EPA is required to regulate carbon dioxide and five other greenhouse gases following a 2007 Supreme Court ruling that the gases qualify as air pollutants under the Clean Air Act. The EPA found in 2009 that the gases pose a threat to public health.
Trump, Pruitt and Energy Secretary Rick Perry deny the consensus among climate scientists that carbon dioxide emissions from human activity are the primary cause of global warming.
Following Pruitt's statement, New York Attorney General Eric Schneiderman vowed to sue the administration.
"By seeking to repeal the Clean Power Plan — especially without any credible plan to replacing it — the Trump administration's campaign of climate change denial continues, once again putting industry special interests ahead of New Yorkers' and all Americans' safety, health, and the environment," he said in a statement.
Environmental groups were already threatening legal action and protests prior to Pruitt's comments on Monday.
"Trump can't reverse our clean energy and climate progress with the stroke of a pen, and we'll fight him and Scott Pruitt in the courts, in the streets, and at the state and local level across America to protect the health of every community," Sierra Club Executive Director Michael Brune said in a statement on Friday.