The new Professional Pilots Union seem to be able to at least discuss the issue sensibly and give good advice, which is a start:
Cabin Air Quality
The Independent Pilots Association (IPA) has done much over the past 5 years to raise awareness of the issue, even to the point of sponsoring medical research. All IPA paying members have been kept well informed on CAQ.
I know which Union I would rather represent my health interests. No question.