26 CFR § 601.602 - Tax forms and instructions.
(a) Tax return forms and instructions. The Internal Revenue Service develops forms and instructions that explain the requirements of the Internal Revenue Code and regulations. The Service distributes the forms and instructions to help taxpayers comply with the law. The tax system is based on voluntary compliance, and the taxpayers complete and return the forms with payment of any tax owed.
(b) Other forms and instructions. In addition to tax return forms, the Internal Revenue Service furnishes the public copies of other forms and instructions developed for use in complying with the laws and regulations. These forms and instructions lead the taxpayer step-by-step through data needed to accurately report information required by law.
(c) Where to get forms and instructions. The Internal Revenue Service mails tax return forms to taxpayers who have previously filed returns. However, taxpayers can call or write to district directors or directors of service centers for copies of any forms they need. These forms are described in Publication 676, Catalog of Federal Tax Forms, Form Letters, and Notices, which the public can buy from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.