A theory or a philosopher on employers monitoring of social media?

[Apple]

I have to write a paper about employers using info found on a person's social media site in making employment and retention decisions and if it's morally permissible or it's violating employee's privacy since social media isn't part of work environment. And I need to find supporting theory or a philosopher. I believe it is violating employee's privacy for employers to use info on personal social media site to make decisions. What would be a good theory in philosophy to support my stand? HELP!