I could see a couple arguments. If the government argues it's an income tax under the 16th amendment you could probably argue somewhat convincingly that it is not yet income.
As a direct tax under Article I Section 8 it would probably be doomed as it would need to be subject to the rule of apportionment -- each state is required to be taxed equal to its percentage of the national population.
In order to survive you would either need to successfully argue that it is income or that it is an indirect tax (think excise taxes, customs duties, etc).
