No references, but I want to throw in two cents.
Labels are information, but in a context. Labeling tuna "dolphin-safe"
without a media campaign to explain driftnets, etc., probably won't make
for social change. Clothes have labels that tell where they are made, and
if consumers know about those countries, their gov'ts and labor practices,
etc, then that label can change buying habits. Most processed food says
which conglomerate made it, and again, that info can help people make
informed purchasing decisions. Usually, we see this only as an organized
boycott.
So, that leads me to start thinking about corporate-owned media and which
stories are allowed to make it out to the general public. The media create
the context within which those labels are read.
My humble suggestion, therefore, would be to look not only at labels and
consumers' attitudes, but also at the context.
ciao
bill