(a) In general. Except in the case of a summons that is a designated or related summons described in section 6503(j), the following rules relating to the suspension of certain periods of limitations apply to all third-party summonses subject to the notice requirements of section 7609(a) and to all John Doe summonses subject to the requirements of section 7609(f).

(b) Intervention in an action to enforce the summons—(1) In general. If a person entitled to notice of a summons under section 7609(a) and § 301.7609-2 with respect to whose liability the summons was issued, or such person's agent, nominee, or other person acting under the direction or control of the person entitled to notice, takes any action to intervene in a proceeding with respect to enforcement of such summons brought pursuant to section 7604, that person's periods of limitations under sections 6501 (relating to assessment and collection) and 6531 (relating to criminal prosecutions) for the tax period or periods that are the subject of the summons are suspended for the period during which such proceeding is pending.

(2) Action to intervene. A person entitled to notice takes any action to intervene in a proceeding to enforce a summons within the meaning of § 301.7609-4(a) on the date when a motion to intervene is filed with the court.

(c) Institution of a proceeding to quash a summons—(1) In general. If a person entitled to notice of a summons under section 7609(a) and § 301.7609-2 with respect to whose liability the summons was issued, or such person's agent, nominee, or other person acting under the direction or control of such person, takes any action described in § 301.7609-4(b) to institute a proceeding to quash such summons, that person's periods of limitations under sections 6501 and 6531 for the tax period or periods that are the subject of the summons are suspended for the period during which such proceeding is pending.

(2) Action to institute a proceeding to quash a summons. A person entitled to notice takes any action to institute a proceeding to quash if he or she files a petition to quash the summons in any district court, regardless of whether the timely filing requirements of section 7609(b)(2)(A) or the notice requirements of section 7609(b)(2)(B) are satisfied. For example, a person entitled to notice takes an action to institute a proceeding to quash a summons for purposes of this section if that person files a petition to quash the summons in district court and notifies the summoned person by sending a copy of the petition by registered or certified mail, but fails to mail a copy of that notice to the appropriate Internal Revenue Service (IRS) person and office.

(d) Summoned party's failure to finally resolve the response to a summons after six months from service—(1) In general. If a third party's response to a summons for which the IRS was required to provide notice to persons identified in the summons, or to a John Doe summons described in section 7609(f), is not finally resolved within six months after the date of service of the summons, the periods of limitations are suspended under sections 6501 and 6531, for the person with respect to whose liability the summons was issued and for any person whose identity is sought to be obtained by a John Doe summons, for the tax period or periods that are the subject of the summons. The suspension shall begin on the date which is six months after the service of the summons and shall end on the date on which there is a final resolution of the summoned party's response to the summons.

(2) Example. The rules of paragraph (d)(1) of this section are illustrated by the following example:

(e) Definitions—(1) Agent, nominee, etc. A person is the agent, nominee, or other person of a person entitled to notice under section 7609(a) and § 301.7609-2, and is acting under the direction or control of the person entitled to notice for purposes of section 7609(e)(1), if the person entitled to notice has the ability in fact or at law to cause the agent, nominee or other person, to take the actions permitted under section 7609(b).

(2) Period during which a proceeding is pending—(i) Intervention in an enforcement proceeding. The period during which the periods of limitations under sections 6501 and 6531 are suspended under section 7609(e)(1) begins on the date any person described in paragraph (b) of this section intervenes in an action to enforce the summons. The periods of limitations remain suspended until all appeals are disposed of, or until the expiration of the period during which an appeal may be taken or a request for further review may be made. The periods of limitations remain suspended for the period during which a proceeding is pending, regardless of compliance (or partial compliance) with the summons during that period. If, following issuance of an order to enforce a third-party summons, a collateral proceeding is brought challenging whether production made by the summoned party fully satisfied the court order and whether sanctions should be imposed against the summoned party for a failure to satisfy that order, the periods of limitations remain suspended until all appeals of the collateral proceeding are disposed of, or until the expiration of the period during which an appeal may be taken or a request for further review of the collateral proceeding may be made. Any collateral proceeding to the original proceeding shall be considered to be a continuation of the original proceeding.

(ii) Proceeding to quash a summons. The period during which the periods of limitations under sections 6501 and 6531 are suspended under section 7609(e)(1) begins on the date any person described in paragraph (c) of this section files a petition to quash the summons in district court. The periods of limitations remain suspended until all appeals are disposed of, or until expiration of the period in which an appeal may be taken or a request for further review may be made. The periods of limitations remain suspended for the period during which a proceeding is pending, regardless of compliance (or partial compliance) with the summons during that period.

(iii) Examples. The rules of paragraph (e)(2) are illustrated by the following examples:

(3) Final resolution of the summoned third party's response to a summons. For purposes of section 7609(e)(2)(B), final resolution with respect to a summoned party's response to a third-party summons occurs when the summons or any order enforcing any part of the summons is fully complied with and all appeals or requests for further review are disposed of, the period in which an appeal may be taken has expired or the period in which a request for further review may be made has expired. The determination of whether there has been full compliance will be made within a reasonable time, given the volume and complexity of the records produced, after the later of the giving of all testimony or the production of all records requested by the summons or required by any order enforcing any part of the summons. If, following an enforcement order, collateral proceedings are brought challenging whether the production made by the summoned party fully satisfied the court order and whether sanctions should be imposed against the summoned party for a failing to do so, the suspension of the periods of limitations shall continue until the summons or any order enforcing any part of the summons is fully complied with and the decision in the collateral proceeding becomes final. A decision in a collateral proceeding becomes final when all appeals are disposed of, the period in which an appeal may be taken has expired or the period in which a request for further review may be made has expired.

(f) Effective/applicability date. This section is applicable on April 30, 2008.