Can a head manager of fast food resturaunt keep employees from socializing with other employees?

It depends on what this manager's rationale is for telling all of you that you can’t associate with co-workers outside of work. Depending on the answer to that, there’s a good chance that’s illegal. For example, if you want to go out to dinner with fellow co-workers but are restricted from doing so because the manager wants to stagger breaks rather than having a bunch of you gone all at once. However, since there is no company prohibition from such socializing, it does not appear that the nature of your job dictates that you not fraternize with fellow employees outside of work (e.g. if you were a security guard or the like). Absent a legitimate business related reason, this manager is most likely wrong to prevent you from socializing with co-workers when off the clock and off work premises. In fact, the National Labor Relations Act prevents employers from interfering with employees discussing wages and working conditions with each other. Further, even if you weren’t talking about work, this type of restriction could be be considered to have a "chilling effect" on your rights and be consdirered to be an unfair labor practice. Bottom line, if this manger is simply trying to control the employees' private lives, then that his directive could likely be a violation of privacy laws, etc. At this point, you can check with your state's department of labor and/or a local employment law attorney.