While entering into a contract with a worker can assist in defining the nature of the working relationship, what it can't do is create one. You cannot classify an employee as an independent contractor simply by drawing up a contract that puts that label on the relationship. Negotiating a contract with an independent contractor or an agency may help to reinforce the validity of the worker's status as an independent contractor by specifying the details of the employment relationship in case a question arises as to the worker's status.
The federal and state governments place a high priority on preventing the misclassification of workers, and therefore, so should you. The scrutiny in this area is constantly intensifying and is not to be taken lightly due to the penalties and fines that can result for non-compliance with employment and tax laws. Use contracts to ensure that your independent contractors are correctly classified as such and not to attempt to misclassify those who are actually your employees!