If its a tax...

...then Obama's health care penalty is unconstitutional, or at least that's what these guys argue. Per David Kopel, their argument comes down to this...

In brief, the argument is: The tax is not an excise tax, and it could not be a constitutional excise tax because it is not uniform. The tax is not an income tax, and it could not be a constitutional income tax, because it is not a tax on derived income. Accordingly, the tax must be a capitation or direct tax. Article I, section 9 provides: “No capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or Enumeration herein before directed to be taken.” The tax is not apportioned, and therefore is contrary to Article I, section 9.