Just because you are called an intern, doesn’t mean that you have to work for free. If you are really working like an employee and the company is the primary beneficiary of your work, you probably should be paid.
In Connecticut, the rule comes from the Second Circuit Court of Appeals which has a 7 part test. It gives employers more leeway when the internship is part of an educational institution.
In Massachusetts, anyone “performing services” while undergoing “training” in an “industry trade or business or branch thereof” is considered to be an employee. See Mass. Lawyers Weekly. So, in Massachusetts, interns and trainees performing services must be paid minimum wage unless they are under a training program in some type of charitable, educational or religious institution.
Interns should not assume that they should always be unpaid!