FICA (Federal Insurance Contributions Act) is the federal law on social security contributions. It is a federal payroll tax paid by both the employee and the employer. The amount of the tax is 6.2% for social security and 1.45% for health insurance.
A non‑resident who does not reside in the USA may be exempt from paying FICA. This includes foreign students, scientists, teachers, researchers, interns, doctors, au pairs, and others working in the USA on F-1, J-1, M-1, Q-1, or Q-2 visas.