What part of the Constitution allows for a tax just for existing?

[Elwar]

After several arguments about the Constitutionality of the income tax the pro-tax people always point to the 16th Amendment, the government has power to lay taxes upon any income...

But in order for ObamaCare to make it through the Supreme Court they had to call it a tax.

But if you have no income, what is taxed? And how is it Constitutional?

[Kluge]

If you have no income, I'd guess you're expected (required?) to go on Medicaid. (or Medicare - I can never remember which is which)

[Hawker]

Government has always been able to levy poll taxes.

[Elwar]

Government has always been able to levy poll taxes.

They got rid of poll taxes quite a while ago:

24th Amendment:
The right of citizens of the United States to vote in any primary or other election for President or Vice President, for electors for President or Vice President, or for Senator or Representative in Congress, shall not be denied or abridged by the United States or any State by reason of failure to pay any poll tax or other tax.

[Hawker]

Government has always been able to levy poll taxes.

They got rid of poll taxes quite a while ago:

24th Amendment:
The right of citizens of the United States to vote in any primary or other election for President or Vice President, for electors for President or Vice President, or for Senator or Representative in Congress, shall not be denied or abridged by the United States or any State by reason of failure to pay any poll tax or other tax.

But the right to levy taxes is still there.  Just one penalty is removed.