This is not really a criminal defense question. I changed the practice area to employment / labor law so you'll be more likely to get a reply.
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They can't in California, because the California State Constitution protects the privacy of Californians, and that protection extends to private employers, not just government agencies. I don't know how things are in Maryland. Perhaps they are backwards. Contact a local lawyer who represents employees. Look for one using the find a lawyer feature of AVVO, or go to Maryland Employment Lawyers Association web site (I've provided a link below). You should be able to get a free phone consult to check whether Maryland law provides any protection for this sort of thing. Question to ponder: how were you damaged by this?
This response creates no attorney client relationship; consult a local lawyer for help if you proceed.
In Maryland employer drug testing is regulated by MD. Code, Health General,. Sec. 17-214. Notice of a positive test result is covered by Sec. 17-214(c). Rights of confidentiality are defined in Sec. 17-214(I). The issue of privacy was discussed at length in a recent decision issued filed as Whyte v. Concentra Health Services, Inc., U.S.D.C., No. ELH-12-3432 (9/24/2013). ("The only point at which the Testing Statute addresses employee privacy is in its provisions governing confidentiality. See H.G. § 17-214(i)(1). Those provisions, however, are concerned with protecting the privacy of the employees’ medical information, not their right to bodily integrity. See id. (prohibiting testing laboratory or physician’s disclosure to employer of “information regarding . . . [t]he use of a nonprescription drug, excluding alcohol, that is not prohibited under the laws of the State; or . . . [t]he use of a medically prescribed drug . . . .”)). Another point to consider is the language of the waiver or consent form filed to authorize the test before it was administered.
The correct answer will depend on the law as it is applied in your State. The outcome on the same facts may vary from State to State. Consult a local attorney.