(a) In general
Any imputed underpayment shall be assessed and collected in the same manner as if it were a tax imposed for the adjustment year by subtitle A, except that—

(1) subchapter B of chapter 63 shall not apply, and

(2) in the case of an administrative adjustment request to which section 6227(b)(1) applies, the underpayment shall be paid and may be assessed when the request is filed.

(b) Limitation on assessment
Except as otherwise provided in this subtitle (other than subchapter B of this chapter), no assessment of an imputed underpayment may be made (and no levy or proceeding in any court for the collection of any amount resulting from such adjustment may be made, begun or prosecuted) before—

(1) the close of the 90th day after the day on which a notice of a final partnership adjustment was mailed, and

(2) if a petition is filed under section 6234 with respect to such notice, the decision of the court has become final.

The preceding sentence shall not apply in the case of a specified similar amount (as defined in subsection (f)(2)).

(c) Premature action may be enjoined
Notwithstanding section 7421(a), any action which violates subsection (b) may be enjoined in the proper court, including the Tax Court. The Tax Court shall have no jurisdiction to enjoin any action under this subsection unless a timely petition has been filed under section 6234 and then only in respect of the adjustments that are the subject of such petition.

(d) Exceptions to restrictions on adjustments

(1) Adjustments arising out of math or clerical errors

(A) In general
If the partnership is notified that, on account of a mathematical or clerical error appearing on the partnership return, an adjustment to an item is required, rules similar to the rules of paragraphs (1) and (2) of section 6213(b) shall apply to such adjustment.

(B) Special rule
If a partnership is a partner in another partnership, any adjustment on account of such partnership's failure to comply with the requirements of section 6222(a) with respect to its interest in such other partnership shall be treated as an adjustment referred to in subparagraph (A), except that paragraph (2) of section 6213(b) shall not apply to such adjustment.

(2) Partnership may waive restrictions
The partnership may at any time (whether or not any notice of partnership adjustment has been issued), by a signed notice in writing filed with the Secretary, waive the restrictions provided in subsection (b) on the making of any partnership adjustment.

(e) Limit where no proceeding begun
If no proceeding under section 6234 is begun with respect to any notice of a final partnership adjustment during the 90-day period described in subsection (b), the amount for which the partnership is liable under section 6225 shall not exceed the amount determined in accordance with such notice.

(f) Failure to pay imputed underpayment

(1) In general
If any amount of any imputed underpayment to which section 6225 applies or any specified similar amount (or any interest or penalties with respect to any such amount) has not been paid by the date which is 10 days after the date on which the Secretary provides notice and demand for such payment—

(A) section 6621(a)(2)(B) shall be applied by substituting "5 percentage points" for "3 percentage points" with respect to such amount, and

(B) the Secretary may assess upon each partner of the partnership (determined as of the close of the adjustment year or, if the partnership has ceased to exist as of such time, the former partners of the partnership as determined for purposes of section 6241(7)) a tax equal to such partner's proportionate share of such amount (including any such interest or penalties, determined after application of subparagraph (A)).

(2) Specified similar amount
For purposes of this subsection, the term "specified similar amount" means—

(A) the amount described in subclause (II) of section 6226(b)(4)(A)(ii) (including any failure to satisfy the requirement of subclause (I) of such section which is treated as a failure to pay such amount under section 6651(i)), and

(B) any amount assessed under paragraph (1)(B) upon a partner which is a partnership.

(3) Proportionate share
For purposes of paragraph (1), a partner's proportionate share is such percentage as the Secretary may determine on the basis of such partner's distributive share. The Secretary shall make determinations under the preceding sentence such that the aggregate proportionate shares so determined total 100 percent.

(4) Coordination with partnership liability
The liability of the partnership for any amount with respect to which a partner is made liable under paragraph (1) shall be reduced upon payment by the partner of such amount. Paragraph (1)(B) shall not apply with respect to any amount after the date on which such amount is paid by the partnership.

(5) S corporations
For purposes of this subsection, an S corporation and its shareholders shall be treated in the same manner as a partnership and its partners.

(6) Rules related to assessment and collection

(A) Deficiency procedures not applicable
Subchapter B shall not apply to any assessment or collection under this paragraph.

(B) Limitation on assessment
Except as otherwise provided in this subtitle, no assessment may be made (or proceeding in court begun without assessment) with respect to any partner with respect to an amount under paragraph (1) after the date which is 2 years after the date on which the Secretary provides the notice and demand referred to in paragraph (1) with respect to such amount.