Do Writers Need a Union?

On the website ThePassiveVoice, commenters bring up trade and labor disputes and organizations, and I think these and class warfare comments I've seen elsewhere are spot-on. Trade fiction and narrative nonfiction authors do not have any meaningful representation. There is no group busting balls on behalf of writers, and there are a lot of balls out there to be busted. Amazon, the Big 5, B&N, Apple, Google ... no one is fighting these people for better terms and pay. The Writers' Guild seems to exist to fight Amazon