Let me be more precise.
Trotsky favored forced labor according to the plan. The argument in his defense is that this is no more coercive than capitalist labor, indeed less so, to the extent that the plan is democratically determined. There are at least two major problems with this: (1) The plan wasn't democratically determined - there wasn't even any intention of trying to formulate it democratically, and it probably could not have been so formulated even if that had been the intention. (2) It is true that under both capitalism and this form of "socialism" the overall economic scheme is determined in an equally undemocratic fashion, but for the *individual* the element of compulsion is far greater under the latter since under the former one at least has some scope of choice over the particular form one's coerced contribution must take. That's the whole reason why the phrase "forced labor" is usually met with repulsion, even by those who have no illusions about capitalist freedom. I say "usually," but of course not by Trotsky, who has no patience for such pacifist-vegetarianism.
SA