Human resource laws are so involved and there are so many.

I have some scenarios to study on my own at the end of my text to help me prepare for an upcoming exam. Human resource laws are so involved and there are so many. Can you please help me with this practice scenario?

You just started your new job as the director of HR for a government contractor. After being there for a few weeks, you notice the employees are periodically drug tested. However, the tests don't appear random and tend to focus on one specific group.

What I need to know is does the drug free workplace act apply to this situation? And if it does, why is that so? Thank you so much for your help.