Federal income tax – 1913
“The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration.”
Basically it is stating that they are not figuring taxes based on state populations. For example if 5% of the United States population lives in a state that does not mean that state will be paying 5% of the taxes.
See: Previous Amendment (Fifteenth Amendment) – Next Amendment (Seventeenth Amendment)