If I’m a social work supervisor with a graduate degree and have proof that 2 employees I supervise are making a higher salary than me, can I sue the agency for unfair wages?

Maybe. The issue is not that your subordinates make more than you, but whether there is a non-discriminatory reason for it--the first thing to bear in mind is that unless you believe that they are paid more than you because of your membership in a specifically protected class of persons--such as because of your race, your gender, your age over 40, your disability, or your religion--the law doesn't care if your subordinates earn more than you. So the first thing hurdle is that unless you are alleging discrimination due to your group or classification, there would be no cause of action.

Even assuming that you are of a different race or gender than these employees, are over 40, are disabled, or have some other grounds to allege discrimination, while you have a graduate degree and are these employees' supervisor, there are still situations under which they could lawfully earn more, such as:

1) More years in service (and so more raises) at this employer;

2) Prior work experience which is germane to their jobs and for which they are compensated in their salary;

3) Performance-based raises in the past;

4) Having been transferred from a higher-paid division/department/jobs but having had their salaries grandfathered;

5) Etc.

This is not to say that you may not have a good case; but you need to first make sure there is no valid reason. When I was first out of lawschool, I was an attorney admitted to the bar of two states who worked at a government agency; I supervised an auditor (someone with only an undergraduate accounting degree) who earned a lot more than me--but he was twenty years my senior, with significantly more time in service, which counted for a great deal at this agency.

If there is no non-discriminatory reason for the discrepancy, however, then you may have a case and should speak in detail about it with an employment law attorney.