I am a law school graduate. What I offer is mere information, not to be construed as forming an attorney client relationship.
can't be:
1. If your hair is clean -- urine test was contaminated because hair tests for up to three months of drug exams and have more weight in court than a urine test.
2. If you alone was given an examination and no one else, you were singled out illegally.
Hence, you need to hire a labor law attorney ASAP to get through this muck and try to get a settlement. You do owe a duty though to attempt to mitigate your damages by seeking same/similar employment.
Try
http://www.attorneypages.com or call your state bar association and ask for lawyer referral.