Privately operated shelters are generally allowed to limit their populations in ways that might surprise you: They can allow people of just one gender to stay there. They can exclude children. They can exclude drug users. If the shelter is committed to keeping out drug users, then it has to be fair and legitimate in figuring out who is using drugs. The most reliable way to be sure that the shelter does not have any drug users is to conduct scientific testing.
If a shelter is testing for drug use just to prevent drug crimes from happening then, depending on whether and how it is connected with the government, it may be violating the Constitution’s Fourth Amendment which requires that investigators (or drug testers) have both 1. probable cause to believe that a particular person has committed a certain crime and 2. a warrant issued by a judge in order to search for evidence connected with the crime. http://law.justia.com/constitution/us/amendment-04/07-probable-cause.html To simply guess that a person coming into a homeless shelter might be drug user would not, without other proof, justify a drug test.
If the shelter is targeting certain individuals or groups for drug testing, then those individuals or groups may have a legal claim of discrimination.
Even if the shelter is testing everyone or else is doing random drug testing that doesn’t target individuals or groups, the drug tests might be seen as invasions of privacy. The ACLU takes a strong stand on this and has won court cases by proving that the entities testing for drug use did not have reasons that outweighed people’s right to have the chemical content of their urine kept private. https://www.aclu.org/other/legislative-briefing-kit-drug-testing Contact your local ACLU office if you want them to consider suing a shelter for its drug testing practices. http://www.aclu.org/affiliates
In most states, if there is any drug testing law at all, it is about when and how employers can test workers for drug use. You can peruse those state laws via Nolo Press at http://www.nolo.com/legal-encyclopedia/free-books/employee-rights-book/chapter5-3.html Even though employers and shelters have separate specific reasons for conducting drug tests, the reasons are probably connected with safety in both settings. So, if you have to argue against a drug testing policy you might want to first see whether you have a state law and then compare the shelter’s policy with it to see if the policy looks like it complies with the law. If you don’t think it does, contact Project H.E.L.P. http://homelesslegalprotection.com/h-e-l-p-locations/ or the National Law Center on Homelessness and Poverty http://www.nlchp.org/contact_us.cfm or your local legal aid office. http://www.lsc.gov