I consider myself a libertarian, because I value personal liberty above any authority.
My observation is that most people who call themselves libertarians do not. Their talk of liberty is merely rationalization of their real position: That the basis of authority is wealth, rather than democracy.
When confronted with the fact that a person is being oppressed by their employment, the answer is simply that they can always find another job. Well, nobody is holding a gun to your head and forcing you to live here. If you feel like the government is that oppressive, you're free to go find another one. You are literally free to leave any time. Oh- but where will you go? Well, is a better company hiring? But you were born here, you served in the military, you own a home? As if millions of workers have not invested years of their life and health in their job.
We live in a society where the government is (theoretically) answerable to the people- Government by consent of the governed. It was created that way in the interest of individual freedom. If you don't like it, it can be changed. The same cannot be said for a corporation- The only way to make them change is through government interference, or by controlling a large enough financial stake to overrule the board.
It's time to think not in terms of governments, but in terms of power. Power corrupts, absolute power corrupts absolutely. In the past several centuries, that power base has shifted from the church, to governments, and then to corporations.
The threat to personal liberty comes from the accumulation of power. Whether that power is amassed by the government, the company, the church or the angry mob is irrelevant.