In some instances media see no difference between professional and personal activity --- they believe that what you do anywhere reflects on your employer anywhere. In other instances there are measures in place if employees cross the line, including disciplinary action that includes termination.
The latest to weigh in is the large U.S.-based Scripps organization. Its policy sets down boundaries for professional and personal social media accounts and guides both with a set of principles.
Unlike some other companies, Scripps recognizes personal accounts have validity --- but only to deal with personal lives, not to commingle them with professional duties. Same goes for the professional accounts --- they're only there to reflect one's work. The company is clear that it will take action
As for the guiding principles on the professional accounts, they're fairly basic and common-sense: guard your reputation, engage, pause before publishing, make it a conversation, and so on.