It can do almost anything it wants to.
Rick Hills, an NYU law professor who appears to specialize in federalism (and does not appear to be a conservative), writes:
I am no friend of the Commerce Clause argument against the individual mandate’s constitutionality…But, in relying on the Taxing power, the Court has failed to offer a coherent purpose-driven reason for the result. It cannot be the case that the feds always can “encourage” people to undertake actions by taxing their inaction: Such a taxing power would render nonsense the basic idea that the enumeration presupposes something not enumerated.
So… what is the limit on the taxing power? Since Kahriger, the usual doctrine has been that the tax must generate revenue. But this test is patently unsatisfactory, because all taxes generate revenue if they are set just below the level at which they would completely prohibit a taxed activity. A tax on same-sex marriages of, say, $1,000 per marriage would presumably generate some revenue — but would it be a constitutional exercise of Congress’ enumerated powers? If so, then the idea of the enumeration is exploded, except as a formalistic obeisance to the text of Article I. Put another way, no sane framer would bother to enumerate powers if the only limit on the federal government’s taxing power is that the tax generate some revenue and that people who wish to avoid the tax can do so through either action or inaction.
So far as I can tell from an initial reading of the 5-vote majority, the Court offers no functional reason whatsoever for its analysis of the taxing power. Indeed, the Court insults our intelligence by describing the conventional analysis of taxation under its prior precedents as somehow “a functional approach” (page 35). Of course, there is nothing “functional” about its definition of the taxing power, if the only relevant factors are the power of a taxed individual to avoid action or inaction that is taxed. If the test is, as Chief Roberts describes it, paying the tax “may often be a reasonable financial decision,” then Congress will have fairly unlimited power to regulate any activity simply by imposing an exaction just short of what it would take to eliminate the activity altogether. If the only other limit is that Congress (or the IRS) cannot “penalize” persons who choose to pay the tax, by stigmatizing them as “outlaws” (page 38), then such a limit is worse than formalistic: It is not even consistent with the precedent (Doremus) upholding the Harrison Narcotics tax.
How is such a taxing power consistent with any sensible notion of enumerating powers? Why would any sane framer, whether Hamilton or Luther Martin, Federalist or Anti-Federalist, ever agree to such an arrangement? The Court does not say.
I’m not a law professor, but my sentiments exactly.