A construction worker gets his pay from non federal contracts in the private sector of on of the several states (such as California). His "income" does not come from a FEDERAL source nor any of the few named in section 861 & operative sections of the Internal Revenue Code. Therefore, his compensation for labor done within that state (geography is a deciding factor too -- jurisdictional) is NOT taxable.
If a citizen refuses to pay this tax, they will often be arrested at point of gun, and put in jail - making it a true definition of slavery.
The abover definition is completely false, because the federal income tax doesn't discriminate between sources of income from government occupations and private labor. See e.g. 26 U.S.C. § 61. Otherwise, how would the federal government be able to fund its operations?