Tomorrow, oral arguments examining the legality of the EPA’s landmark Clean Power Plan (CPP) will be heard before the U.S. Court of Appeals for the D.C. circuit. The CPP is the EPA’s sweeping#Climate Change plan that targets coal-fired power plants that emit the trace gas carbon dioxide (CO2).

Led by West Virginia, 27 states, the coal industry, and at least 100 groups, they are challenging its legality and are suing the Environmental Protection Agency(EPA) and the #Obama administration. The nation’s coal industry, cheap electricity, and the right of the government to ‘coerce’ a state into carrying out duties are all at stake.

The EPA’s Clean Power Plan relies on Section 111(d) of the Clean Air Act. That section, the EPA claims, gives the agency regulatory power to control “non-toxic” emissions like CO2 from power plants. But Section 111(d) also prevents the EPA from regulating emissions if it was already regulating a “source category” under a separate section of the law.

That would be Section 112, which the EPA currently uses to regulate “toxicemissions (like mercury). But in the shuffle to homogenize the House version with the Senate’s, the wording was never clarified. As such, it prevents the EPA from double-regulating an industry.