Environmentalists are promising a battle royale next month as the titans of industry clash with the Obama administration and its activist supporters in the biggest legal battle over climate change to date.

“Just weeks from now, NRDC and its allies will be fighting in the D.C. Circuit Court to defend the Clean Power Plan in one of the most important courtroom battles ever for our climate,” said Rhea Suh, president of the Natural Resources Defense Council, in a Friday message to donors.