As an at-will employee, there is practically nothing you can do in this situation. In Indiana, and throughout the United States, employment law
heavily favors the employer in most situations. Unless the employee has a contract which provides that the employee may only be terminated for cause, the law will hold that the employee's right to work
falls under the At Will
Doctrine. The At Will Doctrine provides that an employer may terminate an employee for any reason whatsoever, even if it is a false reason. The only limitation on this is that an employer may not terminate an employee because of discrimination
based on race, color, religion, sex, military status, national origin, disability, age, or ancestry of the employee.
In your case, you say you were suspended and may be terminated based on a false positive on a drug screen which was not handled properly. Rules regarding chain of custody and proper preservation of the evidence only come into play when we are talking about evidence in a court of law. Here, the company drug screener did not handle the situation properly, but because this is not a case before a court or a criminal investigation, it does not matter. Your employer has the right to terminate you for any or no reason whatsoever.
So, you should stop viewing the improper handling of the specimen as a viable defense, as in the end it has no teeth. Instead, what I would advise you to do is contact the drug screener and ask for the results of your test. Then I would recommend sending in a letter to your employer which points out the the drug screener did not handle the specimen carefully and most importantly, that the positive is a false positive because it was caused by your prescription medication. Attach to the letter a copy of your prescription. This will give your employer a reasonable basis to overlook the drug screen results. You can even go the extra mile and go pay for an independent drug screen yourself, and let the lab know that you are taking the prescription med so that they can note on the screen that any positive is a false positive.