For instance i knew 2 brothers who both worked in a plant here. Both failed drug tests. The private company that owns the plant booted #1 brother that day no questions asked and no re-hire status. Brother #2 worked for a union contractor inside the plant, was sent to rehab and was eligible for rehire 6 months or so after completing the rehab.....
Drugs are usually the grey area in most.
Theft, intentionally harming the buisness, walking off the job without notice. etc are usually the standard grounds for non re hire status...