Nevada wasn’t the first state to approve recreational marijuana usage, but it is the first to make it illegal to discriminate against users.
That’s not the language used in the bill, but that’s what the law does. Instead of leaving it up to an employer to determine if they want a drug free workplace, you have to treat marijuana users as equals to non-users.
New York City has similar legislation which will go into effect shortly after Nevada’s, even though New York doesn’t have legalized recreational marijuana.
There is logic to this change because unlike alcohol, which clears out of your system relatively rapidly; you can test positive for marijuana when you aren’t remotely high.