An employer is required to withhold all types of taxes for resident aliens. Holders of the I–551 Permanent Resident Card ("Green Card") fall into this category. However, employers do not withhold Social Security or Medicare taxes if the alien is an agricultural worker or holds a variety of nonimmigrant visas, such as F-1 (students), H-1B (professionals and technical workers), or Q (cultural exchange visitors).

A nonresident alien is required to complete a W-4 form. When doing so, the person cannot claim exemption from withholding, must state his or her marital status as being single, and in most cases can only claim one allowance.