> How are trade unions consistent with free association?
It should not be against the law for a number of likeminded employees to associate and collectively bargain with their employer. That part is “Freedom of Association”.
> If I have to join a union just to get a job in my area of expertise, how is that free association?
That part isn’t free association. That’s the “closed shop” and IMO it is an odious concept.
That said, it is not unlike the employer subcontracting the labor to another organization — in this case a union — in much the same way as they would subcontract their building security to a security company. Conceptually these are similar scenarios.
Allowing that analogy, if you want to provide security to that company you need to be a member of the security company’s staff. Similarly, if you want to build cars there, you need to belong to the automotive union that has the collective contract for labor there.
So no, the Closed Shop isn’t about Free Association, but it is arguably about the freedom to make contracts and agreements.
That is one good thing about government unions, they cannot force you to join them as a condition of working for the government.
Yet.