Grounds to sue for what? You haven't said if there were any negative implications of the test. Did they not hire you? Talk with an employment attorney in your city about this, to better understand your rights. My guess is that they didn't do anything outside their normal policies, and also might not have done the drug test in-house. Thus, they might have relied on the results from a third-party testing facility. But all of those details can come out when you talk with the employment attorney.
The above is not intended to be legal advice, but may be used for general information. Please contact an attorney for specific help tailored to your needs. www.figgardenlaw.com
In Rhode Island, and except for certain jobs, employment related drug testing is only allowed if the employer complies with RI General Law 28-6.5-1. (Linked to below)
One provision in that law is the employer cannot take any action against you unless the "Positive tests of urine, blood, or any other bodily fluid or tissue are confirmed by a federal certified laboratory by means of gas chromatography/mass spectrometry or technology recognized as being at least as scientifically accurate."
I am not your attorney and I am not giving legal advice. I am giving you general information about the law. To give you legal advice I would first have to learn more about the facts and circumstances of your particular situation. The Rhode Island Supreme Court licenses all lawyers in the general practice of law. The court does not license or certify any lawyer as an expert or specialist in any particular field of practice.