Crooked Timber has an excellent discussion of libertarianism and coercion in the private sphere. I find the section contrasting how libertarians discuss union coercion vs. employer coercion particularly interesting. I recommend everyone take a moment to read over the post for a good overview of the topic, though it is rather lengthy.
(Of course, this viewpoint is inconsistent with any philosophy wishing for a cessation of coercion, since the state used as a check is necessarily coercive. But I think it is undeniable that people experience coercion even when engaging in free contract, trying to define coercion differently doesn't remove the reality of the experience. It simply allows for an internally consistent, coherent philosophy, something which I believe comes at the expense of dealing with reality and with making a philosophy relevant to policy discussions.)