The Patient Protection and Affordable Care Act (aka ObamaCare) includes what it calls an "individual responsibility requirement" that all persons buy health insurance from a private company. Congress justified this mandate under its power to regulate commerce among the several states: "The individual responsibility requirement provided for in this section," the law says, ". . . is commercial and economic in nature, and substantially affects interstate commerce, as a result of the effects described in paragraph (2)." Paragraph (2) then begins: "The requirement regulates activity that is commercial and economic in nature: economic and financial decisions about how and when health care is paid for, and when health insurance is purchased."
In this way, the statute speciously tries to convert inactivity into the "activity" of making a "decision." By this reasoning, your "decision" not to take a job, not to sell your house, or not to buy a Chevrolet is an "activity that is commercial and economic in nature" that can be mandated by Congress.
It is true that the Supreme Court has interpreted the Commerce Clause broadly enough to reach wholly intrastate economic "activity" that substantially affects interstate commerce. But the Court has never upheld a requirement that
individuals who are doing nothing must engage in economic activity by entering
into a contractual relationship with a private company. Such a claim of power is
Professor Barnett also co-authored a more detail analysis of the individual mandate found here. He also wrote an excellent analysis on the constitutionality of the legislation here.
ObamaCare was passed with little regard for the constitutionality of its provisions. Although there is a popular move to repeal the bill the more likely dismantling of the law will come through the courts. With Justice Stevens retiring, the President's Supreme Court nominee takes on a new importance.