The question of whether a worker is an employee or an independent contractor can have very important consequences, as the two categories receive very different treatment under the law. To name only a few differences, there are no federal or state income tax withholding obligations for independent contractors; wage and hour laws do not apply to independent contractors; most anti-discrimination laws do not apply to independent contractors. And, of course, the employer mandate under the Affordable Care Act does not apply in the case of independent contractors. There is a lot riding on the question.
It can sometimes be difficult to predict whether a worker will be deemed an employee or an independent contractor, but there are multiple tests depending upon which area of law is implicated.