The ability of an employer to conduct drug tests depends largely on who the employer is. If it is a public employer, drug tests are likely not allowed, unless it is a corrections officer, an air traffic controller, or another position that requires large amounts of public trust. However, with other employees of the government such as teachers and firefighters, drug tests can only be administered if there is reasonable suspicion that the employee is taking drugs.
It’s a whole other world in the private employers context. If you work for a private company, your rights against drug testing are extremely limited. In this case, an employee must submit to a drug test and can only sue in limited circumstances, such as if the employer violated your off-work privacy, defames your character by telling people you failed the test if you did not, or if the test turns up negative and they take action against you when, in fact, the test results were wrong.
In these cases, you can sue, but again, it is expensive, and unfortunately, often not worth the battle.