ninety-day letter.Statutory notice of a tax deficiency sent by the IRS to a taxpayer. • During the 90 days after receiving the notice, the taxpayer must pay the taxes (and, if desired, seek a refund) or challenge the deficiency in tax court. IRC (26 USCA) §§ 6212, 6213. — Also written 90-day letter. — Also termed notice of deficiency; deficiency notice; tax-deficiency notice. Cf.

THIRTY-DAY LETTER. [Cases: Internal Revenue 4542. C.J.S. Internal Revenue § 650.]

[Blacks Law 8th]