Generally, if an employer does not withhold income taxes, social security, and Medicare from your pay, you are being treated as an independent contractor (self-employed person). If you believe an employee relationship exists and you cannot resolve this matter with your employer, you should submit a Form SS-8 (PDF), Determination of Employee Work Status for Purposes of Federal Employment Taxes and Income Tax Withholding. The factors used to determine if an employer-employee relationship exists are covered in Chapter 2 of Publication 15-A (PDF), Employer's Supplemental Tax Guide.

If your status as an employee is not at issue, it may be that you are in a category of employment whose earnings are not defined as wages under U.S. federal tax and social security law. Find out from your employer the reason that social security and Medicare taxes and income taxes are not being withheld from your pay. If you have further questions, contact the IRS at 800-829-1040 or visit an IRS walk-in office for assistance.

References:

• Form SS-8 (PDF), Determination of Employee Work Status for Purposes of Federal Employment Taxes and Income Tax Withholding
• Publication 15-A (PDF), Employer's Supplemental Tax Guide
• Publication 1779 (PDF), Independent Contractor or Employee

Source: www.irs.gov