Robert Nozick, answered from the texts and cited to the page.
Taxation of earnings from labor is on a par with forced labor.1 The argument: taking some hours of someone's labor is equivalent to taking the products of those hours, since money and the goods money buys are produced by labor.2 If the state compels some persons to work some hours for the benefit of others — through compulsory non-paid service, say — we would recognize this as forced labor.
Taxation of earnings does precisely the same thing in different form: the tax represents hours of labor whose product the laborer is required to turn over to the state for transfer to others. The distinction between "taxing wages" and "compelling labor" is not a moral distinction but a procedural one. The position follows directly from the entitlement theory and from self-ownership: if I own myself, I own my labor; if I own my labor, I own its products; and the involuntary appropriation of those products, whether by direct conscription or by taxation, is on a moral par.345
However, neither view is correct. The fact chat others intentionally intervene, in violation of a side constraint against aggression, to threaten force to limit the alternatives, in this case to paying taxes or (presumably the worse alternative) bare subsistence, makes the taxation system one of forced labor and distinguishes it from other cases of limited choices which are not forcings.Anarchy, State, and Utopia, p. 170
Those who doubt that this extension can be carried through, and who draw the line here at taxation of income from labor, will have to state rather complicated patterned historical principles of distributive justice, since end-state principles would not distinguish sources of income in any way.Anarchy, State, and Utopia, p. 171
The likelihood is small that any actual freely-arrived-at set of holdings fits a given pattern; and the likelihood is nil that it will continue to fit the pattern as people exchange and give. From the point of view of an entitlement theory, redistribution is a serious matter indeed, involving, as it does, the violation of people's rights.Anarchy, State, and Utopia, p. 169
When end-result principles of distributive justice are built into the legal structure of a society, they (as do most patterned principles) give each citizen an enforceable claim to some portion of the total social product; that is, to some portion of the sum total of the individually and jointly made products.Anarchy, State, and Utopia, pp. 171–172
Building a fence around a territory presumably would make one the owner of only the fence (and the land immediately underneath it). Why does mixing one's labor with something make one the owner of it? Perhaps because one owns one's labor, and so one comes to own a previously unowned thing that becomes permeated with what one owns. Ownership seeps over into the rest.Anarchy, State, and Utopia, p. 175
The most quoted, most contested, and most provocative formulation in ASU. Many readers regard it as a reductio of libertarianism — taxation manifestly is not the same as forced labor, and a doctrine that says it is must be wrong. Defenders respond that this reaction is exactly the moralized intuition Nozick was trying to dislodge: we have been raised to accept taxation as natural and to see forced labor as outrageous, and Nozick is asking what the moral difference is. Cohen takes the formulation seriously and constructs the most sustained reply, which is also a sustained attack on the underlying self-ownership thesis. The line remains the canonical provocation of libertarian political philosophy.