I agree with Oliver Willis. I guess I can understand the importance to paid bloggers who work for candidates, parties, organizations, or corporations, of having their needs taken care of.
However, for most of us, blogging is not something we are paid for or ever plan to be paid for. A small number of bloggers may make enough income from ads to blog full time, but in that case, who needs a union? In fact, I find the suggestion insulting to unions for REAL workers. Perhaps the blogosphere can worry about helping to start unions for real professions that need them. Salaried writers at educational development houses perhaps (heh), or any number of real jobs (yeah, I said it) that need union representation. Its insulting that labor unions would even consider adding bloggers, when so many other professions are lacking any adequate support. All I know, is that my recent emails to publishers and writer's unions have been ignored. Perhaps if I told them I was blogger, they would have written back.
Like Oliver said, a REALLY BAD IDEA.