There's a nice paper by Bengt Holmstrom (Review of Economic Studies, 1999) that has a story about inefficienty high (but still voluntary) work effort in the absence of a policy that limits effort, such as a maximum hours restriction. The idea is that no one worker can cut back effort to the efficient level without appearing to be of low ability, and this is true even though employers know that all the workers aren't as good as they appear (their high output is largely due to the fact that they work too hard, not to how good they are).