This is an excerpt from Form 990 Instructions: Appendix G. It is relevant to most 501(c)(3) charities. Linked here
Appendix G: Use of Form 990 or 990-EZ To Satisfy State Reporting Requirements
Some states and local government units will accept a copy of Form 990 or 990-EZ in place of all or part of their own financial report forms. The substitution applies primarily to section 501(c)(3) organizations, but some of the other types of section 501(c) organizations are also affected. If the organization uses Form 990 or 990-EZ to satisfy state or local filing requirements, such as those under state charitable solicitation acts, note the following discussions.
The organization can consult the appropriate officials of all states and other jurisdictions in which it does business to determine their specific filing requirements. Doing business in a jurisdiction can include any of the following: (a) soliciting contributions or grants by mail or otherwise from individuals, businesses, or other charitable organizations; (b) conducting programs; (c) having employees within that jurisdiction; (d) maintaining a checking account; or (e) owning or renting property there.
Some or all of the dollar limitations applicable to Form 990 or 990-EZ when filed with the IRS may not apply when using Form 990 or 990-EZ in place of state or local report forms. Examples of the IRS dollar limitations that do not meet some state requirements are the normally $50,000 gross receipts minimum that creates an obligation to file with the IRS and the $100,000 minimum for listing independent contractors in Form 990, Part VII, Section B, or Form 990-EZ, Part VI, line 51.
State or local filing requirements may require the organization to attach to Form 990 or 990-EZ one or more of the following: (a) additional financial statements, such as a complete analysis of functional expenses or a statement of changes in net assets; (b) notes to financial statements; (c) additional financial schedules; (d) a report on the financial statements by an independent accountant; and (e) answers to additional questions and other information. Each jurisdiction may require the additional material to be presented on forms they provide. The additional information does not have to be submitted with the Form 990 or 990-EZ filed with the IRS.
Even if the Form 990 or 990-EZ that the organization files with the IRS is accepted by the IRS as complete, a copy of the same return filed with a state will not fully satisfy that state's filing requirement if (1) required information is not provided, including any of the additional information discussed above, or (2) the state determines that the form was not completed by following the applicable Form 990 or 990-EZ instructions or supplemental state instructions. In such case, the state may ask the organization to provide the missing information or to submit an amended return.
To ensure that all organizations report similar transactions uniformly, many states require that contributions, gifts, grants, similar amounts, and functional expenses be reported according to the AICPA industry audit and accounting guide, Not-for-Profit Organizations (New York, NY, AICPA, 2003), supplemented , as applicable, by Standards of Accounting and Financial Reporting for Voluntary Health and Welfare Organizations (Washington, DC, National Health Council, Inc., 1998, 4th edition).
Even though donated services and facilities may be reported as items of revenue and expense in certain circumstances, many states and the IRS do not permit the inclusion of those amounts in Form 990, Parts VIII and IX, Form 990-EZ, Part I, or (except for such donations by a governmental unit) in Schedule A (Form 990 or 990-EZ). The optional reporting of donated services and facilities is discussed in the instructions for Part III for Forms 990 and 990-EZ.
If the organization submits supplemental information or files an amended Form 990 or 990-EZ with the IRS, it must also send a copy of the information or amended return to any state with which it filed a copy of Form 990 or 990-EZ originally to meet that state's filing requirement. If a state requires the organization to file an amended Form 990 or 990-EZ to correct conflicts with the Form 990 or 990-EZ instructions, the organization must also file an amended return with the IRS.