In an earlier career I worked on water issues related to the Clean Water Act. I cannot remember the exact ratio but for water issues that extend into regulating seasonal wetlands and navigable streams, it is something like 100 pages of EPA regs for << 10 pages of law passed by Congress. And given the penchant of lawyers to sue, a whole bunch of case law to back up the EPA regulations accumulates over time (or when the EPA loses, the regulations change). And sometimes it is an environmental advocate group suing the EPA or some other govt entity to enforce the law and the regulations.
I do not know what a FSM is but there is a lot of case law for the legal basis for the EPA to regulate greenhouse emissions under the authority of the Clean Air Act. This article is very vague about the issue so perhaps details will come out over time and maybe the case has merit.
For some context:
https://www.epa.gov/nsr/clean-air-act-permitting-greenhouse-gases
https://www.washingtonpost.com/politics/supreme-court-limits-epas-ability-to-regulate-greenhouse-gas-emissions/2014/06/23/c56fc194-f1b1-11e3-914c-1fbd0614e2d4_story.html
There is also a wikipedia article on the topic.
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