The “Constitutional right” line will be used when employers enforced their ban on pot use even in a “legalized” America.
Yet tobacco is banned by some employers (even in the off hours because of insurance costs) and I see no major court cases.
There have already been court cases that have held up firings because smokers are not a protected class.....yet. I know of few employers who won’t hire you if they find nicotine in your drug screen.