It says in Article 1, Section 8
“To lay and Collect taxes, duties, imposts and excises, to pay the debts and provide for the Common defence and general welfare” with no other qualifications than that “all duties, imposts and excises, shall be UNIFORM throughout the United states, that no capitation or other direct tax shall be laid unless in proportion to numbers ascertained by a census or enumeration taken on the principles prescribed in the Constitution, and that “no tax or duty shall be laid on articles exported from any state.”
U.S. Treasury Dept’s International Trade Data System http://www.itds.treas.gov/printglossaryfrm.html defines excise taxes as “taxes on the manufacture, sale, or CONSUMPTION of goods, or upon licenses to pursue certain occupations, or upon corporate privileges,” which, they explain, in current usage covers about everything besides income taxes.
If we are “required” to buy insurance, this mandate is essentially then a 100% tax on a a good that we have to consume, an excise tax. We are mandated to consume it and mandated that we have to expend the cost of doing so. If the government then gives some families a credit for the same mandated consumption, then it is not uniform as stated in our Constitution.