26 U.S.C. § 3501: Collection and payment of taxes

(a) General ruleThe taxes imposed by this subtitle shall be collected by the Secretary and shall be paid into the Treasury of the United States as internal-revenue collections. (b) Taxes with respect to non-cash fringe benefitsThe taxes imposed by this subtitle with respect to non-cash fringe benefits shall be collected (or paid) by the employer at the time and in the manner prescribed by the Secretary by regulations.