The Federal Insurance Contributions Act (FICA) is a critical federal payroll tax that funds Social Security and Medicare programs, requiring both employers and employees to contribute 7.65% each (15.3% total) on wages up to specific limits. For international companies expanding to the US, understanding FICA compliance is essential—the IRS collected $120.2 billion in unpaid employment tax assessments in 2024, with the Trust Fund Recovery Penalty holding business owners personally liable for 100% of unpaid taxes.