Since I can't sleep anyway, I started looking up some things about collective bargaining and found this excellent FAQ.
http://clear.uhwo.hawaii.edu/CB-FAQ.html#Q1
Frankly, I don't see how what they've done is legal. The National Labor Relations Act seems pretty clear to me. The only "gotcha" could be the line at the end.. that it applies to members of unions in the private sector and members of unions that represent both public and private employees. It looks like AFSCME is the *the* public employee union for federal, state and city employees. So... they take ONE private employee group in and they become a union that represents both, right? I know, probably not that simple, but it seems they can get around this somehow.