According to Ideal Bite, a backpack that isn't made from PVCs and is made in the U.S. can be hard to find. They suggest Earthpak as an alternative, which makes backpacks for kids and bags for adults (including bags for birding):
Earthpak offers bags that are made of 98% recycled materials, 100% made in the U.S.A., and with seams that are amazingly stronger than the major manufacturers' bags. The environmentally conscious manufacturing process turns discarded plastic soda bottles into a valuable commodity.I'd love to have a tour of one of their factories and talk to the workers. No mention of whether these are union factories, of course, which probably means they're not.
Via Ideal Bite