Hempel V. U.S‪.‬

The Internal Revenue Code's Anti-Injunction Act generally forbids courts to restrain the Internal Revenue Service (IRS) from assessing*fn1 or collecting a tax. 26 U.S.C. § 7421(a) (1988).*fn2 One exception to this rule arises when the IRS fails to send the taxpayer a statutorily required notice of deficiency, or "90-day letter," prior to assessment; in such a case, an injunction may issue. See id. §§ 6212(a), 6212(c), 6213(a), 7421(a).*fn3 If, however, the taxpayer waives his or her right to a deficiency notice, the general rule applies and neither assessment nor collection may be enjoined. See 26 U.S.C. § 6213(d) (authorizing taxpayer to waive notice).*fn4