I, Joseph R. Biden Jr., do hereby grant a full, complete, and unconditional pardon to all current United States citizens and lawful permanent residents who, on or before the date of this proclamation, committed or were convicted of the offense of simple possession of marijuana, attempted simple possession of marijuana, or use of marijuana, regardless of whether they have been charged with or prosecuted for these offenses on or before the date of this proclamation
You can be fired for failing a drug test even if the drugs are legal.
Nicotine is a drug. Never ever heard anyone being fired for that.
And while it is true, there could be other rules that companies may enforce (don’t operate heavy machinery while drunk, for example), government contractors have to react simply because the drug is on the list, and the test is positive. BY LAW, even if it has zero impact or positive impact on productivity.