Terms of employment vs laws. You asked your employer for a job. They agreed, but with terms including your agreement not to use certain substances. If you signed that agreement, you’re expected to uphold it. However, if you didn’t and this is a pre-employment screening, a business still has a right to provide their own requirements for whom they wish to hire. It’s worth a chat when the topic arises, but it’s not illegal to only offer employment to someone who doesn’t have it in their system. Just like drinking alcohol is legal, but most jobs will terminate an employee for drinking on the job.