Internal Revenue Code Section 6033. Returns by exempt organizations.
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(a) Organizations required to file
(1) In general
Except as provided in paragraph (3), every organization exempt from taxation under section 501 (a) [see note below in blue text] shall file an annual return, stating specifically the items of gross income, receipts, and disbursements, and such other information for the purpose of carrying out the internal revenue laws as the Secretary may by forms or regulations prescribe, and shall keep such records, render under oath such statements, make such other returns, and comply with such rules and regulations as the Secretary may from time to time prescribe; except that, in the discretion of the Secretary, any organization described in section 401 (a) may be relieved from stating in its return any information which is reported in returns filed by the employer which established such organization.
Note: Section 501(a) exempts certain types of organizations from federal income taxes. Namely: Organizations described by 501(c), 501(d), and 401(a). Section 401(a) refers to qualified pension, profit-sharing, and stock bonus plans.
Note 2: See subsection (i) further down this page regarding the Form 990-N electronic postcard requirement, and subsection (j) regarding automatic revocation of tax-exempt status.
(2) I have omitted paragraph 2, as it does not directly address the Form 990 filing requirement.
(3) Exceptions from filing
(A) Mandatory exceptions
Paragraph (1) shall not apply to—
(i) churches, their integrated auxiliaries, and conventions or associations of churches,
(ii) any organization (other than a private foundation, as defined in section 509 (a)) described in subparagraph (C), the gross receipts of which in each taxable year are normally not more than $5,000, or
(iii) the exclusively religious activities of any religious order.
(B) Discretionary exceptions
The Secretary may relieve any organization required under paragraph (1) (other than an organization described in section 509 (a)(3)) to file an information return from filing such a return where he determines that such filing is not necessary to the efficient administration of the internal revenue laws.
(C) Certain organizations
The organizations referred to in subparagraph (A)(ii) are—
(i) a religious organization described in section 501 (c)(3);
(ii) an educational organization described in section 170 (b)(1)(A)(ii);
(iii) a charitable organization, or an organization for the prevention of cruelty to children or animals, described in section 501 (c)(3), if such organization is supported, in whole or in part, by funds contributed by the United States or any State or political subdivision thereof, or is primarily supported by contributions of the general public;
(iv) an organization described in section 501 (c)(3), if such organization is operated, supervised, or controlled by or in connection with a religious organization described in clause (i);
(v) an organization described in section 501 (c)(8); and
(vi) an organization described in section 501 (c)(1), if such organization is a corporation wholly owned by the United States or any agency or instrumentality thereof, or a wholly-owned subsidiary of such a corporation.
New Form 990-N Electronic Postcard Requirement enacted in 2006:
(i) Additional notification requirements
Any organization the gross receipts of which in any taxable year result in such organization being referred to in subsection (a)(3)(A)(ii) or (a)(3)(B)—
(1) shall furnish annually, in electronic form, and at such time and in such manner as the Secretary may by regulations prescribe [Form 990-N], information setting forth—
(A) the legal name of the organization,
(B) any name under which such organization operates or does business,
(C) the organization’s mailing address and Internet web site address (if any),
(D) the organization’s taxpayer identification number,
(E) the name and address of a principal officer, and
(F) evidence of the continuing basis for the organization’s exemption from the filing requirements under subsection (a)(1), and
(2) upon the termination of the existence of the organization, shall furnish notice of such termination.
(j) Loss of exempt status for failure to file return or notice
(1) In general
If an organization described in subsection (a)(1) or (i) fails to file an annual return or notice required under either subsection for 3 consecutive years, such organization’s status as an organization exempt from tax under section 501 (a) shall be considered revoked on and after the date set by the Secretary for the filing of the third annual return or notice. The Secretary shall publish and maintain a list of any organization the status of which is so revoked.
(2) Application necessary for reinstatement
Any organization the tax-exempt status of which is revoked under paragraph (1) must apply in order to obtain reinstatement of such status regardless of whether such organization was originally required to make such an application.
(3) Retroactive reinstatement if reasonable cause shown for failure
If, upon application for reinstatement of status as an organization exempt from tax under section 501 (a), an organization described in paragraph (1) can show to the satisfaction of the Secretary evidence of reasonable cause for the failure described in such paragraph, the organization’s exempt status may, in the discretion of the Secretary, be reinstated effective from the date of the revocation under such paragraph.