You have taken that out of context. THE PARABLE OF THE WORKERS IN THE VINEYARD. You left out the relevant part of 20:16 "So the last will be first, and the first will be last." There are many people in control of the union doing evil things, but this does not mean that the union has always been evil or always will be. There is hope for those in control, and this is the true meaning of this parable.
You have taken that out of context. THE PARABLE OF THE WORKERS IN THE VINEYARD. You left out the relevant part of 20:16 "So the last will be first, and the first will be last." There are many people in control of the union doing evil things, but this does not mean that the union has always been evil or always will be. There is hope for those in control, and this is the true meaning of this parable.
Read the rest of the thread. Note that I never speak of the union members as evil (although some are). The very concept of a union is anti-biblical.
Jesus taught from parables using everyday truths to demonstrate the truths of the kingdom of God. If the parables were false then the gospel would be false.
While you are correct that the parable deals with entry into the Kingdom, it also establishes the truthfulness that an owner has the right to do with his property as he wishes. (otherwise all who heard it would say, but an owner doesn't have control of his property and therefore the connection you are trying to make is invalid) Since a union interferes with that right (via strike and all unions strike or hold some other sort of labor action that harms the business) then unions are anti-biblical.
This is the only scripture I've found that comes near to addressing the topic of unions and it speaks against them.