A cartel is a set of profit seeking firms in a specific industry who hold enough market influence to dictate price. It is the coordinated actions of an oligopoly to manipulate the market. You don't need to own the full market, you just need to be able to influence the market as a whole.
A union is, on a very surface level similar to a cartel, but unions are monopolies of labor, and do not represent the firms themselves.
They are both attempts to manipulate markets through group decision making, but even academically, they aren't seen as the same thing. There is a reason that cartel formation is very illegal while union formation is a protected right.
that's like saying OPEC isn't a cartel because you can still get oil from russia or canada.
>it can fire it's entire workforce and rehire
isn't that union-busting and/or illegal?
> isn't that union-busting and/or illegal?
It's supposed to be, but it's often the case that corporations are not penalized to a sufficient amount (or at all) to deter this. We've seen many cases where it's cheaper for the corporation to pay these fines and continue doing what they are doing - in that sense the current laws are ineffective.