There are several ways to find out if you feel you are being
black balled but since this would be a difficult accusation to
prove, the one I would chose as being the best is consulting with a
private investigator. The one I was impressed with was ICS, phone
number 800-828-9198, they have a free consultation and will let you
know if your case is of merit. Also they would be considered an
impartial witness to your case. You can hire them to pose as a
potential employer and contact your employer you believe is
blackballing you, they will more than likely tape the conversation.
Blackballing can be as little as a gesture, a tone of voice or by
direct slander. Remember also, as with most cases, the longer you
wait to prove your case, the harder it will be to win. Good luck to
you.