This question is only a hypothetical
. When one tests postitive in a drug test, the testing company will contact you with a series of questions. The questions are designed to determine if legal use or other drug use could have triggered the positive.
If one were in mexico and enjoyed a bit of the local flavor and then were tested back in the US, can you be terminated. I'm sure that you can, but what do you think?
I have tried to think of other examples where an action is legal in a different country but not in the US but have struggled to come up with another that would be similar to this situation.
How about sex laws in other countries? Some places have lower age of consent laws? Do we prosecute those people who are returning to the US after the "crime" was committed in a different country.