The OSHA Hazard Communication Standard requires that ALL hazardous materials be labeled.   Container labels in HAZCOM areas must be attached to the container itself.  

Hazardous chemicals in portable containers which are for the immediate use of the employee who performs the transfer is the exception to this rule.   These containers do not have to be labeled unless they are left unattended or are still present at the end of the employees shift.   If they are left unattended at any time, they must be labeled.