It's legal, if the bill originates in Congress. Which it has: HR 4646, the "Debt Free America Act."
More info here:
ClickyHere's a summary:
QUOTE
Debt Free America Act - States as purposes of this Act the raising of sufficient revenue from a fee on transactions to eliminate the national debt within seven years and the phasing out of the individual income tax. Amends the Internal Revenue Code to impose a 1% fee, offset by a corresponding nonrefundable income tax credit, on transactions that use a payment instrument, including any check, cash, credit card, transfer of stock, bonds, or other financial instrument. Defines "transaction" to include retail and wholesale sales, purchases of intermediate goods, and financial and intangible transactions. Establishes in the legislative branch the Bipartisan Task Force for Responsible Fiscal Action to review the fiscal imbalance of the federal government and make recommendations to improve such imbalance. Provides for expedited consideration by Congress of Task Force recommendations. Repeals after 2017 the individual income tax, refundable and nonrefundable personal tax credits, and the alternative minimum tax (AMT) on individuals. Directs the Secretary of the Treasury to: (1) prioritize the repayment of the national debt to protect the fiscal stability of the United States; and (2) study and report to Congress on the implementation of this Act.
[emphasis added]
In a nutshell, it's designed to replace the current income-tax system with something like the VAT system used in some European countries. It's been stuck in the House Appropriations committee since February.