I would recommend that you get with a lawyer immediately. Get all your records gathered up to confirm all these facts. I would also supply all this information to your union representative immediately. Talk to your lawyer, but I'd guess that a letter from your doctor saying that this drug is safe or does not affect your job performance would a big help.
You should contact these folks at NAMA (National Alliance of Methadone Advocates) about Methadone Discrimination:
Their web sites states: "Discrimination is a major obstacle for anyone who has ever used drugs. While some legislation has been enacted which protects former addicts and methadone patients, there still remain many areas where methadone patients are not protected. NAMA works to inform methadone patients of their rights and to provide support to those who have been victims of discrimination."
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