39 U.S. Code § 3685 - Filing of information relating to periodical publications
(a) Each owner of a publication having periodical publication mail privileges shall furnish to the Postal Service at least once a year, and shall publish in such publication once a year, information in such form and detail and at such time as the Postal Service may require with respect to—
(2) the identity of the corporation and stockholders thereof, if the publication is owned by a corporation;
(4) the extent and nature of the circulation of the publication, including, but not limited to, the number of copies distributed, the methods of distribution, and the extent to which such circulation is paid in whole or in part; and
(5) such other information as the Postal Service may deem necessary to determine whether the publication meets the standards for periodical publication mail privileges.
The Postal Service shall not require the names of persons owning less than 1 percent of the total amount of stocks, bonds, mortgages, or other securities.
(b) Each publication having such mail privileges shall furnish to the Postal Service information in such form and detail, and at such times, as the Postal Service requires to determine whether the publication continues to qualify for such privileges.