An employer generally has the right to provide policies which govern the workplace. It is permissible for an employer to have a specific policy which forbids employees from “friending” clients. It might be virtually impossible to enforce and might engender bad feelings from a client, but an employer is generally free to do so. See the earlier answer on off-duty conduct in the work place. As for the friend argument, an employee certainly can make this argument and, for that reason, employers need to consider whether it is a good idea to have this restriction. Some employees and clients might take offense and this could present a practical problem. From a legal perspective, an employee can make this argument but that does not change the fact that an employer is generally free to provide policies to govern the workplace.