||Costco's drug policy is available at: https://wss6a.unicru.com/hirepro/C409/COST_FORM_Drug_And_Alcohol_Policy.html
Costco has a drug test and an alcohol test. The drug test checks for "marijuana, opiates, cocaine, amphetamines, phencyclidine (PCP)...or their metabolites," but Costco's policy requires that "Employees must be free of the presence of unauthorized substances at all times, so they are capable of exercising good judgment and safe work behavior." In their policy, they define "unauthorized substances" as "any alcohol, illegal drug, or any legal prescription drug used in a manner for which it was not intended or prescribed, or the use of another person’s prescription drug." Either the drug test or alcohol test or both can be required in the following situations. Pre-Employment (including returning employees), Reasonable Suspicion (of on-the-job intoxication), and Post-Accident. Obviously such acts as refusing a drug test, diluting/tampering with a urine sample, sale/possession of drugs/alcohol (open bottles) while at work violate the policy. Tests are taken by breath, saliva, or urine. I have no personal experience with this policy yet, but the application process for employment is online, and their drug policy is online, and there is no mention of random testing, so if you are randomly tested or discriminately tested, you probably have a case against them.