The Constitution – Article I, section 8, clause 1

Spending Clause

“The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises…”

General Welfare Clause

“…to pay the Debts and provide for the common Defence and general Welfare of the United States…”

Uniformity Clause

“…but all Duties, Imposts and Excises shall be uniform throughout the United States…”