department wants a generic signon

I am constantly being asked to create a single network signon for use with shared computers in our company. For example, a signon called “shipping” for anyone in the shipping dept to use on the computer they all share. I always demand that each employee have their own signon and that they logon and off each time they use the computer. Has anyone compiled a list of reasons why this is best practice and can someone state the Sarbanes-Oxley type laws that would demand this of a publicly held company?