The common law rules that determine if someone is an independent contractor or an employee now fall into three categories:
Behavioral: Does the company control or have the right to control what the worker does and how the worker does his or her job?
Financial: Are the business aspects of the worker’s job controlled by the payer? (these include things like how worker is paid, whether expenses are reimbursed, who provides tools/supplies, etc.)
Type of Relationship: Are there written contracts or employee type benefits (i.e. pension plan, insurance, vacation pay, etc.)? Will the relationship continue and is the work performed a key aspect of the business?
(From the IRS: see this)
The IRS site states specifically that no one factor stands alone in making this determination, but that all factors must be considered. Consider all the factors, and document each of the factors. If you're still unsure, give us a call, and we can help you answer the questions to make the determination.