Employers are required by law to make deductions from the pay of their employees for federal income tax, for Social Security tax under the Federal Insurance Contribution Act (FICA), and for Medicare tax. The government provides detailed tables for the computation of these withholding amounts. Internal Revenue Service (IRS) Publication 15, Circular E, Employer's Tax Guide, provides details and may be obtained by writing or calling the IRS or on the Internet at http://www.irs.gov/formspubs.