(1) Except as otherwise provided in the Nebraska Revenue Act of 1967, a notice of a proposed deficiency determination shall be mailed to the taxpayer within three years after the return was filed. Except as otherwise provided in the Nebraska Revenue Act of 1967, no deficiency shall be assessed or collected with respect to the year for which the return was filed unless a notice of a proposed deficiency determination is mailed within three years after the return was filed or the period otherwise fixed.

(2) If the taxpayer omits from Nebraska taxable income an amount properly includable therein which is in excess of twenty-five percent of the amount of taxable income stated in the return or a corporate return omits a properly includable member of the unitary group as defined in section 77-2734.04, a notice of a deficiency determination may be mailed to the taxpayer within six years after the return was filed. A notice of deficiency determination based on the omission of a member of a unitary group shall be limited to the increase in the tax caused by including the omitted member. For purposes of this subsection, there shall not be taken into account any amount which is omitted in the return if such amount is disclosed in the return, or in a statement attached to the return, in a manner adequate to apprise the Tax Commissioner of the nature and amount of such item and the manner in which such item would affect the computation of Nebraska taxable income.

(3) If no return is filed or a false and fraudulent return is filed with intent to evade the income tax imposed by the Nebraska Revenue Act of 1967, a notice of deficiency determination may be mailed to the taxpayer at any time.

(4) If a taxpayer fails to comply with the requirement of section 77-2775 by not reporting a change or correction increasing his or her federal adjusted gross income, taxable income, or tax liability or a change or correction which is treated in the same manner as if it were a deficiency determination for federal income tax purposes, or by not reporting a change or correction in income taxable in or tax credit allowable by any state to the extent required by the Tax Commissioner by regulation, or in not filing an amended return, a notice of deficiency determination based on a complete examination of the tax liability for the tax years involved may be mailed to the taxpayer at any time.

(5) If the taxpayer, pursuant to section 77-2775, reports a federal change or correction or a state change or correction, files an amended return increasing his or her federal adjusted gross income, taxable income, or tax liability, or reports a change or correction which is treated in the same manner as if it were a deficiency for federal income tax purposes, a notice of a deficiency determination based on a redetermination of Nebraska tax liability to reflect the change or correction may be mailed at any time within two years after such report or amended return was filed.

(6) When, before the expiration of the time prescribed in this section for the mailing of a notice of deficiency determination, both the Tax Commissioner and the taxpayer have consented in writing to the mailing after such time, the notice of deficiency determination may be mailed at any time prior to the expiration of the period agreed upon. The period so agreed may be extended by subsequent agreement in writing made before the expiration of the period previously agreed upon.

An agreement between the taxpayer and the Internal Revenue Service providing for the extension of the period for the mailing of a notice of deficiency determination of federal income taxes shall constitute an agreement with the Tax Commissioner to extend the period for assessment of income taxes under the Nebraska Revenue Act of 1967 through the ending date shown on the federal agreement. A copy of all such agreements and extensions thereof shall be filed with the Tax Commissioner within thirty days after their execution. If the copy of the extension agreement with the Internal Revenue Service is not filed pursuant to this subsection, the notice of deficiency determination for such taxable year may be mailed at any time within one year of the discovery of the extension by the Tax Commissioner.

(7) For purposes of this section, an income tax return filed before the last day prescribed by the Nebraska Revenue Act of 1967 for the filing thereof, determined without regard to any extension of time to file the return, shall be deemed to be filed on such last day. If a return or withholding tax for any period ending with or within a calendar year is filed before April 15 of the succeeding calendar year, such return shall be deemed to be filed on April 15 of such succeeding calendar year.

(8) When it becomes necessary for the Tax Commissioner to apply for a court order under subsection (2) of section 77-27,109 for the production of books, papers, records, or memoranda or the testimony of any person, the period for the mailing of a notice of deficiency determination shall be tolled from the date the Tax Commissioner first applies to the appropriate court for the order until the last date on which the information or testimony contained in the application for the court order is obtained by the Tax Commissioner.

This subsection shall not apply if the court finds that the information is not relevant to the determination of the tax liability, the information was provided prior to the filing of the application, or the application was not filed within the time period otherwise provided in this section for the mailing of a notice of deficiency determination.

(9) Any extension for an item of entity income that is signed on behalf of the entity or by the entity's tax matters person for federal income tax purposes shall extend the time period during which a notice of deficiency could be mailed to the partners, shareholders, or members of the entity with respect to any item of entity income.