The companies add that the same things they've done to shift to clean power aren't going away under the Clean Power Plan. You can still build your own facilities or buy electricity from eco-friendly providers, they say.

It's relatively easy for these companies to lend their support, since they have the cash and motivations to switch to emissions-free energy. It's not so simple for states like West Virginia, where coal and other polluting energy sources still dominate. Even so, the brief could help remind the court that tougher emissions controls aren't necessarily bad for business.