Section 6166(k)(2) provides:
(k) Cross references
. . . . . . . .
For special lien (in lieu of bond) in the case of an extension under this section, see section 6324A.
§6324A. Special lien for estate tax deferred under section 6166
(a) General rule
In the case of any estate with respect to which an election has been made under section 6166, if the executor makes an election under this section (at such time and in such manner as the Secretary shall by regulations prescribe) and files the agreement referred to in subsection (c), the deferred amount (plus any interest, additional amount, addition to tax, assessable penalty, and costs attributable to the deferred amount) shall be a lien in favor of the United States on the section 6166 lien property.
(b) Section 6166 lien property
(1) In general
For purposes of this section, the term "section 6166 lien property" means interests in real and other property to the extent such interests-
(A) can be expected to survive the deferral period, and
(B) are designated in the agreement referred to in subsection (c).
(2) Maximum value of required property
The maximum value of the property which the Secretary may require as section 6166 lien property with respect to any estate shall be a value which is not greater than the sum of-
(A) the deferred amount, and
(B) the required interest amount.
For purposes of the preceding sentence, the value of any property shall be determined as of the date prescribed by section 6151(a) for payment of the tax imposed by chapter 11 and shall be determined by taking into account any encumbrance such as a lien under section 6324B.
(3) Partial substitution of bond for lien
If the value required as section 6166 lien property pursuant to paragraph (2) exceeds the value of the interests in property covered by the agreement referred to in subsection (c), the Secretary may accept bond in an amount equal to such excess conditioned on the payment of the amount extended in accordance with the terms of such extension.
The agreement referred to in this subsection is a written agreement signed by each person in being who has an interest (whether or not in possession) in any property designated in such agreement-
(1) consenting to the creation of the lien under this section with respect to such property, and
(2) designating a responsible person who shall be the agent for the beneficiaries of the estate and for the persons who have consented to the creation of the lien in dealings with the Secretary on matters arising under section 6166 or this section.
(d) Special rules
(1) Requirement that lien be filed
The lien imposed by this section shall not be valid as against any purchaser, holder of a security interest, mechanic's lien, or judgment lien creditor until notice thereof which meets the requirements of section 6323(f) has been filed by the Secretary. Such notice shall not be required to be refiled.
(2) Period of lien
The lien imposed by this section shall arise at the time the executor is discharged from liability under section 2204 (or, if earlier, at the time notice is filed pursuant to paragraph (1)) and shall continue until the liability for the deferred amount is satisfied or becomes unenforceable by reason of lapse of time.
Even though notice of a lien imposed by this section has been filed as provided in paragraph (1), such lien shall not be valid-
(A) Real property tax and special assessment liens
To the extent provided in section 6323(b)(6).
(B) Real property subject to a mechanic's lien for repairs and improvement
In the case of any real property subject to a lien for repair or improvement, as against a mechanic's lienor.
(C) Real property construction or improvement financing agreement
As against any security interest set forth in paragraph (3) of section 6323(c) (whether such security interest came into existence before or after tax lien filing).
Subparagraphs (B) and (C) shall not apply to any security interest which came into existence after the date on which the Secretary filed notice (in a manner similar to notice filed under section 6323(f)) that payment of the deferred amount has been accelerated under section 6166(g).
(4) Lien to be in lieu of section 6324 lien
If there is a lien under this section on any property with respect to any estate, there shall not be any lien under section 6324 on such property with respect to the same estate.
(5) Additional lien property required in certain cases
If at any time the value of the property covered by the agreement is less than the unpaid portion of the deferred amount and the required interest amount, the Secretary may require the addition of property to the agreement (but he may not require under this paragraph that the value of the property covered by the agreement exceed such unpaid portion). If property having the required value is not added to the property covered by the agreement (or if other security equal to the required value is not furnished) within 90 days after notice and demand therefor by the Secretary, the failure to comply with the preceding sentence shall be treated as an act accelerating payment of the installments under section 6166(g).
(6) Lien to be in lieu of bond
The Secretary may not require under section 6165 the furnishing of any bond for the payment of any tax to which an agreement which meets the requirements of subsection (c) applies.
For purposes of this section-
(1) Deferred amount
The term "deferred amount" means the aggregate amount deferred under section 6166 (determined as of the date prescribed by section 6151(a) for payment of the tax imposed by chapter 11).
(2) Required interest amount
The term "required interest amount" means the aggregate amount of interest which will be payable over the first 4 years of the deferral period with respect to the deferred amount (determined as of the date prescribed by section 6151(a) for the payment of the tax imposed by chapter 11).
(3) Deferral period
The term "deferral period" means the period for which the payment of tax is deferred pursuant to the election under section 6166.
(4) Application of definitions in case of deficiencies
In the case of a deficiency, a separate deferred amount, required interest amount, and deferral period shall be determined as of the due date of the first installment after the deficiency is prorated to installments under section 6166.
6324A Comment 1: See United States v. Mary Carol S. Johnson et al, 224 F.Supp. 3d 1220 (December 1, 2016) for an explanation of how a section 6324A consensual lien functions. [This link takes you to the District Court opinion itself.] Section 6324A is a taxpayer election. If the taxpayer's election satisifes the stautory requirements shown above, the IRS cannot reject the lien.