26 USC 6011 - General requirement of return, statement, or list

(a) General rule 
When required by regulations prescribed by the Secretary any person made liable for any tax imposed by this title, or with respect to the collection thereof, shall make a return or statement according to the forms and regulations prescribed by the Secretary. Every person required to make a return or statement shall include therein the information required by such forms or regulations.
(b) Identification of taxpayer 
The Secretary is authorized to require such information with respect to persons subject to the taxes imposed by chapter 21 or chapter 24 as is necessary or helpful in securing proper identification of such persons.
(c) Returns, etc., of DISCS and former DISCS and former FSC’s 

(1) Records and information 
A DISC, former DISC, or former FSC (as defined in section 922 as in effect before its repeal by the FSC Repeal and Extraterritorial Income Exclusion Act of 2000) shall for the taxable year
(A) furnish such information to persons who were shareholders at any time during such taxable year, and to the Secretary, and
(B) keep such records, as may be required by regulations prescribed by the Secretary.
(2) Returns 
A DISC shall file for the taxable year such returns as may be prescribed by the Secretary by forms or regulations.
(d) Authority to require information concerning section 912 allowances 
The Secretary may by regulations require any individual who receives allowances which are excluded from gross income under section 912 for any taxable year to include on his return of the taxes imposed by subtitle A for such taxable year such information with respect to the amount and type of such allowances as the Secretary determines to be appropriate.
(e) Regulations requiring returns on magnetic media, etc. 

(1) In general 
The Secretary shall prescribe regulations providing standards for determining which returns must be filed on magnetic media or in other machine-readable form. The Secretary may not require returns of any tax imposed by subtitle A on individuals, estates, and trusts to be other than on paper forms supplied by the Secretary.
(2) Requirements of regulations 
In prescribing regulations under paragraph (1), the Secretary
(A) shall not require any person to file returns on magnetic media unless such person is required to file at least 250 returns during the calendar year, and
(B) shall take into account (among other relevant factors) the ability of the taxpayer to comply at reasonable cost with the requirements of such regulations.

Notwithstanding the preceding sentence, the Secretary shall require partnerships having more than 100 partners to file returns on magnetic media.

(f) Promotion of electronic filing 

(1) In general 
The Secretary is authorized to promote the benefits of and encourage the use of electronic tax administration programs, as they become available, through the use of mass communications and other means.
(2) Incentives 
The Secretary may implement procedures to provide for the payment of appropriate incentives for electronically filed returns.
(g) Disclosure of reportable transaction to tax-exempt entity 
Any taxable party to a prohibited tax shelter transaction (as defined in section 4965 (e)(1)) shall by statement disclose to any tax-exempt entity (as defined in section 4965 (c)) which is a party to such transaction that such transaction is such a prohibited tax shelter transaction.
(h) Income, estate, and gift taxes 
For requirement that returns of income, estate, and gift taxes be made whether or not there is tax liability, see subparts B and C.