I had a very similar experience as a young manager in a phone company. The team member was a much loved member of the team by many, yet there was a large number of personal  international long distance calls charged to the company. When placed on warning, one of the employee's tactics was to attempt to appeal to the the rest of the team - because, after all, we were a phone company. The final discussion was not pleasant and still haunts me today, even though I had strong counseling from HR about the action that must be taken to resolve the situation.