Wages are financial compensation for labor. Thus a wage tax is a labor tax. This Wiki is a long list of tax protest cases. This section deals with progressive taxation and labor tax arguments:
http://en.wikipedia.org/wiki/Tax_protester_constitutional_arguments#Progressive_taxation
The Fed is not in control of wages and unemployment per se, but it does need to see a rebound in the real sector of the economy (employment and wage growth) so workers can pay back their leveraged debts to the financial sector and banking community.
The image I have of the economy is the old man behind the curtain in the Wizard of Oz, pulling various levers, and perhaps not really in control of the complex machinery. Look at this forumula again:
(G - T) = (S - I) + (M - X)
where G is spending set by Congress in budget policy, and can include efforts to stimulate job creation via fiscal stimulus, T is tax policy set by Congress but is also function of the economy in terms of revenue collected, S is savings set by consumers and households, I is investment made by financial intermediaries and businesses, M is imports and X is exports.
In a recession the taxes naturally go down, if the government spends money to help support the economy, G goes up, but to keep from dumping all that G into the base money, the treasury sells bonds so that government impact on the banking sector is neutral. This must occur to allow the Fed some modicum of control over the money supply. So there are many levers in action at a given time and no one is in control of the complex system. The "free market" is not free either ... but that's another discussion.
Edit: please note the correction in post #53 by mheslep!