[cfn]

"A union: some sellers of labor merge into a single legal entity, and it becomes illegal for some purchasers of labor to buy from alternate suppliers."

I have seen references to this many times. Is this true in the States? I was once a teacher (not in the States) and did not have to sign up to any union. Apart from lawyers and medical personel and maybe a few other "special" professions you don't have to belong to a union to offer your services - at least here in the EU.

[yummyfajitas]

Yes. It is illegal for the employer to fire union workers and replace them with non-union workers. It is illegal to hire new workers at wages lower than the union wage, and in many states to even hire non-union workers.

Unionization is by employer, not by profession, though a few professions (e.g. managers) do lack the ability to gain legal protections by unionizing.