Baseball: The Union

I just read an article in ESPN the magaizne and, the article that i was ready was an-anoymanous person in the MLB was speaking up about steriods (if you want me to post the article i will, because it is a great article). And one of the things that he brought up was the union of the league.

What exactly is the Union there for? And what does the Union do? Does it protect the MLB players? Does it protect the owenrs of the league? Why do we the MLB players pay for a Union when their voice isnt even heard?

i for one would appreciate it if you could post that article would be an interesting read