[jiggyboy]

The unions argued that the law is unconstitutional because 1) it takes the property of labor unions without just compensation

Pretty foul, making the claim that union dues yet to be paid are already yours.

[KarlInOhio]

Maybe the property is the worker, it I thought the thirteenth amendment already covered that.

The unions argued that the law is unconstitutional because 1) it takes the property of labor unions without just compensation – a Fifth Amendment violation; 2) because it interferes with their First Amendment right of association; and 3) because it takes away liberty from union officials.

It's interesting that they said that without the slightest hint of irony. Those same three arguments could be used to argue much more strongly why forced unionization should be illegal everywhere. It takes away the workers' property. It interferes with the workers' rights to freely not associate with the union. And it takes away liberty from the workers.