Libertarians frequently complain that when a government taxes some of its citizens in order to help others, it is forcing them to behave altruistically. And obviously, we are meant to think, that use of force is morally objectionable. But what exactly makes taxation objectionable? One answer that many libertarians supply is that forcing some people to benefit others is wrong because it involves forced labour. The underlying thought seems to be that there is something morally troubling about making some people work for others. In this article I scrutinize this thought. After describing two different kinds of taxation, I show how the libertarian argument about taxes depends on a distinction between posing a threat to other people and failing to help them. This brings us to the moral bedrock of the argument that taxation is forced labour, namely the idea that no one has a right to force you to do something unless you pose a threat to other people. The bulk of my article is devoted to showing (1) that this idea cannot deliver the conclusion that libertarians want because it conflicts with other things that libertarians believe; and (2) once you give up on that idea, it turns out that taxation to benefit others is not necessarily wrong by libertarian standards.