"Have unionized" as in, have formed a group to represent themselves collectively? Or, as in all QA developers at Blizzard now have to be a dues-paying member of this new QA union?

What strikes out at me is that only 19 of the 350 people at the company are unionizing. It's as though someone like specifically release engineers are going on strike, and 80+% of other developers are not. What keeps the company from just reassigning building releases to the other 80% of the developers?