You need to pra copy of your F, J M or Q visa (those which are exempt from Social Security) and a copy of your immigration paperwork showing that your Visa Status is valid (I-20 or DS-2019, for example).You cite IRC Section 3121(b)(19) indicating that this section excludes nonresidents in this status from social security. Indicate that your employer incorrectly withheld FICA while you were a nonresident in exempt status.