26 U.S.C. § 4411

(a) In general There shall be imposed a special tax of $500 per year to be paid by each person who is liable for the tax imposed under section 4401 or who is engaged in receiving wagers for or on behalf of any person so liable. (b) Authorized persons Subsection (a) shall be applied by substituting “$50” for “$500” in the case of— (1) any person whose liability for tax under section 4401 is determined only under paragraph (1) of section 4401(a), and (2) any person who is engaged in receiving wagers only for or on behalf of persons described in paragraph (1).