Presumably automakers are suing California for the inverse thereof—the Dormant Commerce Clause—à la Southern Pacific Co. v. Arizona, saying such authority is actually reserved exclusively to the federal government as an exception to states' general police powers: https://en.wikipedia.org/wiki/Dormant_Commerce_Clause
Peoples heads will fall off if the Supreme Court starts undoing all its prior decisions that rely on it.
The connection to interstate commerce was based on the totality of the wheat he grew, not just the excess portion of it that he claimed wasn't part of interstate commerce. And notably, despite all FUD to the contrary, subsistence farming of wheat for personal/non-commercial consumption was legal at the time. That's why they had there was a threshold in the first place; to protect non-commercial wheat farming.
Can't do anything like that with emissions regulations.
https://www.techdirt.com/2022/02/07/kia-subaru-disable-usefu...
The issue is called the "Dormant Commerce Clause" [2], which is the idea that one state can't place "undue burdens" on interstate commerce. California can't just ban all imports from Texas, or vice versa. But courts have generally upheld health and safety laws, like California's car emissions laws or Hawaii's very strict agricultural products import restrictions --- but only if it is narrowly-tailored and there is a compelling state interest. Hawaii has a very compelling state interest in keeping its unique biodiversity, while California has a compelling state interest in keeping the valley of asphalt known as Los Angeles free of smog. There isn't really a good bright line test or definition in existing precedent of what "compelling state interest" means when it must be balanced against "balkanization" [3] by these kinds of laws, so many are hoping SCOTUS uses this case to make a clear definition.
But it is likely that this kind of law would be seen more as a morality regulation than health and safety. California argued that it was not an attempt to legislate moral issues in other states, but more of a health and safety regulation:
> Mongan [California state solicitor] pushed back on some of the hypotheticals about state laws that would condition the sale of products on a company’s general health care or labor practices. He told Barrett that Proposition 12 is “focused on the production of goods that are coming into” California, rather than on company-wide policies. “I think we would all recognize,” Mongan said, that it would be problematic if states can condition the sales of those products on restrictions of wholly unrelated out-of-state purchasers.” [3]
[1] https://www.scotusblog.com/case-files/cases/national-pork-pr...
[2] https://en.wikipedia.org/wiki/Dormant_Commerce_Clause
[3] https://www.scotusblog.com/2022/10/california-law-on-sale-of...