26 USC 6041 - Information at source

(a) Payments of $600 or more 
All persons engaged in a trade or business and making payment in the course of such trade or business to another person, of rent, salaries, wages, premiums, annuities, compensations, remunerations, emoluments, or other fixed or determinable gains, profits, and income (other than payments to which section 6042 (a)(1), 6044 (a)(1), 6047 (e), 6049 (a), or 6050N (a) applies, and other than payments with respect to which a statement is required under the authority of section 6042 (a)(2), 6044 (a)(2), or 6045), of $600 or more in any taxable year, or, in the case of such payments made by the United States, the officers or employees of the United States having information as to such payments and required to make returns in regard thereto by the regulations hereinafter provided for, shall render a true and accurate return to the Secretary, under such regulations and in such form and manner and to such extent as may be prescribed by the Secretary, setting forth the amount of such gains, profits, and income, and the name and address of the recipient of such payment.
(b) Collection of foreign items 
In the case of collections of items (not payable in the United States) of interest upon the bonds of foreign countries and interest upon the bonds of and dividends from foreign corporations by any person undertaking as a matter of business or for profit the collection of foreign payments of such interest or dividends by means of coupons, checks, or bills of exchange, such person shall make a return according to the forms or regulations prescribed by the Secretary, setting forth the amount paid and the name and address of the recipient of each such payment.
(c) Recipient to furnish name and address 
When necessary to make effective the provisions of this section, the name and address of the recipient of income shall be furnished upon demand of the person paying the income.
(d) Statements to be furnished to persons with respect to whom information is required 
Every person required to make a return under subsection (a) shall furnish to each person with respect to whom such a return is required a written statement showing
(1) the name, address, and phone number of the information contact of the person required to make such return, and
(2) the aggregate amount of payments to the person required to be shown on the return.

The written statement required under the preceding sentence shall be furnished to the person on or before January 31 of the year following the calendar year for which the return under subsection (a) was required to be made. To the extent provided in regulations prescribed by the Secretary, this subsection shall also apply to persons required to make returns under subsection (b).

(e) Section does not apply to certain tips 
This section shall not apply to tips with respect to which section 6053 (a) (relating to reporting of tips) applies.
(f) Section does not apply to certain health arrangements 
This section shall not apply to any payment for medical care (as defined in section 213 (d)) made under
(1) a flexible spending arrangement (as defined in section 106 (c)(2)), or
(2) a health reimbursement arrangement which is treated as employer-provided coverage under an accident or health plan for purposes of section 106.
(g) Nonqualified deferred compensation 
Subsection (a) shall apply to
(1) any deferrals for the year under a nonqualified deferred compensation plan (within the meaning of section 409A (d)), whether or not paid, except that this paragraph shall not apply to deferrals which are required to be reported under section 6051 (a)(13) (without regard to any de minimis exception), and
(2) any amount includible under section 409A and which is not treated as wages under section 3401 (a).