But it’s not. There are tons and tons of “union laws” that treat unions very differently than any other entity.
Some of these laws hurt unions, others help.
For example, a union contract can’t require an employer to hire only union members.
That would create a situation where people would apply to the union first, and if they union accepted them, then they apply for the job.
That would give unions too much power, so it’s not allowed.
Another law forbids sympathy strikes. Unions can only strike against their own employers, not in sympathy with other strikers.
Modern labor law also seeks to discourage strikes by using a war-game like approach to negotiating. Maybe a good idea, maybe not. But certainly not something that happens for non-union orgs.
If we adopted a “hands off” approach to unions, we could easily wind up with insanely powerful unions.
If 2% of the working population went on strike simultaneously, the economy would stop working quickly.
So general strikes are very illegal, even though they are 100% in accord with libertarian ideology.