There is no indication that witnesses are being called to testify to the same overtact, and the accused are most certainly not confessing in open court.
As such, the petitioner argued that this violated his Fifth Amendment rights to due process because it convicts a person for mere association and not some overt criminal act.
Given that Karzai has not indicted a single senior official of his own government, U.S. officials are skeptical that he will act without overt American pressure.
It was difficult enough for the previous Congress to pass the ACA. Although the act imposes other taxes, an overt tax of the size needed to do the same job as the mandate would have been politically unpalatable.