Law: Congress is given taxing authority by the Constitution, therefore Congress can tax your income any way choose.
But, a more clear cut method would have been to raise taxes by $750 and then give tax credits to those who choose to purchase health insurance. Then it would be a choice that the libertarians could have just ignored.
Don't forget, it's the health insurance companies who wanted this law. The cartel is the sole beneficiary in a system where buyers are mandated to purchase a product.