Today's argument at the US Supreme Court on the Patient Protection and Affordable Care Act concerns whether the "penalty" assessed under 26 U.S.C. §5000A against individuals who do not meet the minimum coverage provisions is a "tax" for the purposes of the Anti-Injunction Act.
The Anti-Injunction Act (26 U.S.C. §7421) provides that "Except as provided in sections 6015(e), 6212(a) and (c), 6213(a), 6225(b), 6246(b), 6330(e)(1), 6331(i), 6672(c), 6694(c), 7426(a) and (b)(1), 7429(b), and 7436, no suit for the purpose of restraining the assessment or collection of any tax shall be maintained in any court by any person, whether or not such person is the person against whom such tax was assessed." In other words, an individual cannot bring a suit to enjoin the Government from collecting or assessing a tax, and must instead wait until that tax is assessed against him.
This first day of argument, accordingly, is to determine whether or not the Supreme Court even has jurisdiction to hear this case --- inasmuch as the "penalty" arising under the PPACA does not even take effect until 2014, if the "penalty" is a "tax", the Anti-Injunction Act would apply. Only individuals who have actually been assessed the "penalty" could bring a suit, and only then after they have met the administrative procedures required for any tax litigation.
An example of a nominal "penalty" that is considered to be a "tax" for the purposes of the Anti-Injunction Act is the Trust Fund Recovery Penalty that arises under 26 U.S.C. §6672. See, e.g., Kelly v. Lethert, 362 F.2d 629 (8th Cir. 1966).
The merit and amicus briefs on the Anti-Injunction Act are available at http://www.americanbar.org/publications/preview_home/11-398_Anti-InjuntionAct.html.
For more information about the Anti-Injunction Act, and tax collection generally, please refer to William D. Elliott, Federal Tax Collections, Liens, and Levies, (2d ed. 1995), available in print in the Library (KF6313 .E45 1995) and on Westlaw (WGL-COLLECT).