Labor Dept. defines rules, criteria for unpaid internships
After a series of complaints and negative media portrayals that have accused businesses of misusing unpaid interns, the United States Labor Department have created a new and more clearly defined list of guidelines for when business can use unpaid interns and when they must pay minimum wage. To qualify for an unpaid internship a position must be demonstrably for the benefit of the intern, must be akin to an educational training situation, and the company must not derive immediate benefit from the training of the intern. Additionally, no regular employees can be displaced by an unpaid intern (the intern must be supervised by existing staff), the employer and the intern must come to a clear agreement that wages will not be awarded to the intern, and the intern cannot be necessarily guaranteed a position with the company when the internship is finished.
See "Labor Dept. defines rules, criteria for unpaid internships", Doug Staglin, USA Today, April 22, 2010