[gojomo]

This problem, if it arose, can rather quickly self-correct. If people choose not to work at all at the offered rate, you offer more, until you have the workers you need. (Similarly, if you need better workers, you offer more, as long as it is still profitable to do so.)

[Drbble]

What if people band together into a sort of Union, and agree (in a binding way, with punishment for defectors) as a group (through some sort of majority vote, since consensus is impossible in a large group) to demand a certain wage?

You'd have... a republic with a minimum wage law.

[gojomo]

Indeed, that's what we have. That doesn't refute the idea that the minimum wage law is destructive to general welfare (and especially the welfare of those specifically unemployed because of it). It just means it's a popular destructive law, like many other price controls.