What does UPS do when it finds a package containing marijuana?

Immediately stop the progress of the package, give it to a supervisor. A hazardous materials designated responder has to come pick it up and report it to the police while checking to see if other packages were shipped at the same time (and flagging those packages so when they are scanned, they will notify the loader that the package needs to be given to a designated responder. From there, they track the package back to the location which it was shipped from, and begin an investigation of who shipped the package.