26 C.F.R. § 301.6311-1 : Internal Revenue — INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY — PROCEDURE AND ADMINISTRATION — PROCEDURE AND ADMINISTRATION —COLLECTION —GENERAL PROVISIONS —1 - Payment by check or money order

(a) Authority to receive -
(1) In general.
(i) District directors, Service Center directors, and Compliance Center directors (director) may accept checks or drafts drawn on any financial institution incorporated under the laws of the United States or under the laws of any State, the District of Columbia, or any possession of the United States, or money orders in payment for internal revenue taxes, provided the checks, drafts, or money orders are collectible in United States currency at par, and subject to the further provisions contained in this section. The director may accept the checks, drafts, or money orders in payment for internal revenue stamps to the extent and under the conditions prescribed in paragraph (a)(2) of this section. A check or money order in payment for internal revenue taxes or internal revenue stamps should be made payable to the United States Treasury. A check or money order is payable at par only if the full amount thereof is payable without any deduction for exchange or other charges. As used in this section, the term "money order" means:
(a) U.S. postal, bank, express, or telegraph money order;
( b ) money order issued by a domestic building and loan association (as defined in section 7701(a)(19)) or by a similar association incorporated under the laws of a possession of the United States;
( c ) a money order issued by such other organization as the Commissioner may designate; and
( d ) a money order described in subdivision (ii) of this subparagraph in cases therein described. However, the director may refuse to accept any personal check whenever he or she has good reason to believe that such check will not be honored upon presentment.
(ii) An American citizen residing in a country with which the United States maintains direct exchange of money orders on a domestic basis may pay his tax by postal money order of such country. For a list of such countries, see section 171.27 of the Postal Manual of the United States.
(iii) If one check or money order is remitted to cover two or more persons' taxes, the remittance should be accompanied by a letter of transmittal clearly identifying-
(a) Each person whose tax is to be paid by the remittance;
(b) The amount of the payment on account of each such person; and
(c) The kind of tax paid.
(2) Payment for internal revenue stamps. The director may accept checks, drafts, and money orders described in paragraph (a)(1) of this section in payment for internal revenue stamps. However, the director may refuse to accept any personal check whenever he or she has good reason to believe that such check will not be honored upon presentment.
(b) Checks or money orders not paid -
(1) Ultimate liability. The person who tenders any check (whether certified or uncertified, cashier's, treasurer's, or other form of check or draft) or money order in payment for taxes or stamps is not released from his or her liability until the check, draft, or money order is paid; and, if the check, draft, or money order is not duly paid, the person shall also be liable for all legal penalties and additions, to the same extent as if such check, draft, or money order had not been tendered.
(2) Liability of financial institutions and others. If any certified, treasurer's, or cashier's check, or other guaranteed draft, or money order, is not duly paid, the United States shall have a lien for the amount of such check or draft upon all assets of the financial institution on which drawn, or for the amount of such money order upon the assets of the issuer thereof. The unpaid amount shall be paid out of such assets in preference to any other claims against such financial institution or issuer except the necessary costs and expenses of administration and the reimbursement of the United States for the amount expended in the redemption of the circulating notes of such financial institution. In addition, the Government has the right to exact payment from the person required to make the payment.
(c) Payment in nonconvertible foreign currency. For rules relating to payment of income taxes and taxes under the Federal Insurance Contributions Act in nonconvertible foreign currency, see section 6316 and the regulations thereunder.
(d) Financial institution. For purposes of section 6311 and this section, financial institution includes but is not limited to-
(1) A bank or trust company (as defined in section 581);
(2) A domestic building and loan association (as defined in section 7701(a)(19));
(3) A mutual savings bank (including but not limited to a mutual savings bank as defined in section 591(b));
(4) A credit union (including both state and federal credit unions, and including but not limited to a credit union as defined in section 501(c)(14)); and
(5) A regulated investment company (as defined in section 851(a)).

26 C.F.R. §301.6311-1

32 FR 15241, 11/3/1967, as amended by T.D. 7188, 37 FR 12795, 6/29/1972; T.D. ATF-33, 41 FR 44038, 10/6/1976; T.D. 8595, 60 FR 20899, 4/28/1995; T.D. 8969, 66 FR 64743, 12/14/2001