ranxer:
Congress reserves the right to tax any transfer of funds, including payment for labor.
See section 1 of the Internal Revenue Code for the law that says that income tax is levied on every individual in the United States. It should be on the Internet. It may be long and dense, but just do a quick search for the word "income" or "taxable income".
The reason these people get stonewalled when they say "show us the law!" is because everyone in the government knows they're just being stupid. Every single case of tax protest like this that has gone to court has been not just shot down, but ridiculed by federal judges. They've gotten past the point where they're willing to humor people.
http://evans-legal.com/dan/tpfaq.html