Earlier quoted context omitted.
They don't really have to do drug tests though. Should they for example install monitoring in employees cars to make sure they never speed?
I don't mean to defend the FBI's activites, I just mean to note that if your reason for being is "opposing X", then it's reasonable that you check your employees for X. The FBI opposes drugs big time. It doesn't care about people speeding in cars.
First: If the FBI opposes drugs: then they should at least as strongly oppose nicotine and (in particular) alcohol, too. Oh, you mean drugs that are by some historic accident illegal.
Second: Do the cybersecurity jobs one does at the FBI have any property that will prevent former pot smokers doing them? If not, it's simply a discrimination.