President Obama's sweeping anti-climate change proposal, which mandates states to reduce greenhouse gases by 30 percent over the next 20 years, is facing an early legal challenge.

Although Obama's policy for power plant regulation has yet to be finalized or adopted by the Environmental Protection Agency (EPA,) big coal companies are already fighting back against the proposed emissions limits for existing power plants.

On Thursday, a federal appeals court in Washington, D.C. is set to hear oral arguments in this case. Murray Energy Corp., the largest private coal mining company in the nation, is asking the court to block the EPA from completing its regulation legislation and making the rule final. The company claims that the climate rule would dramatically reduce the use of coal for power generation, and as a result, harm its business.

"As the stakes are so high, and delay will waste enormous amounts of industry, state, and federal resources and result in increased coal fired power plant retirements that cannot be later remedied, this petition requests an extraordinary writ in aid of this court's undoubted jurisdiction over EPA's mandate," the company wrote in a brief to the court, reports Politico.

Opponents of the rules, which include West Virginia and 11 coal-dependent states, also note that the EPA has already implemented cutbacks to mercury and other hazardous air pollutants. Therefore, they argue that the proposed climate change rules are illegal since the 1990 Clean Air Act forbids "double regulation" of power plants.

"This is clearly an illegal attempt by the Obama EPA to impose irrational cap-and-tax mandates," which Congress had rejected, said Gary Broadbent, counsel for Murray Energy, according to the Los Angeles Times.

If implemented, Obama's initiative is expected to close hundreds of coal plants and expand renewable energy sources such as wind and solar.

"These rules are a big deal," said Thomas Lorenzen, a former attorney with the Justice Department. "They could make a fundamental change in how we produce power in this country and move us away from coal and toward natural gas and renewables and nuclear energy."