31 C.F.R. § 203.20 – Investment account requirements.

(a) Additions. Treasury will invest funds in obligations of collector depositaries that accept term investments, investor depositaries, or retainer depositaries. Such obligations will be in the form of open-ended interest-bearing notes, or in the case of term investments, interest-bearing notes maintained for a predetermined period of time, and additions and reductions will be reflected on the books of the TSC.
1. (1) PATAX. The TSC will credit the TIP main account balance as stated in § 203.16(a) for an investor or retainer depositary processing tax deposits through PATAX.
2. (2) EFTPS—(i) ACH debit and ACH credit. The TSC will credit a depositary's TIP main account balance, and credit the depositary's reserve account if capacity exists, for the amount of EFTPS ACH debit and credit entries on the day such entries settle.
3. (ii) Fedwire ® value and non-value transactions. The TSC will credit a depositary's TIP main account balance if capacity exists, throughout the day on the day of settlement, for the amount of Fedwire ® value and non-value transactions. In the case of Fedwire ® value transactions, the depositary's reserve account will also be credited.
(b) Additional offerings. Other funds from Treasury may be offered from time to time to depositaries participating in the investment program through direct investments, SDIs, term investments, or other investment programs.
(c) Withdrawals. The amount of a TIP main account balance or SDI account balance is payable on demand without prior notice. The TSC will make calls for payment at the direction of the Secretary. On behalf of Treasury, the TSC will debit the depositary's reserve account on the day specified in the call for payment.
(d) Interest. The TIP main account balance and the SDI account balance bear interest at the TT&L rate of interest. Such interest is payable by a charge to the depositary's reserve account in the manner prescribed in the procedural instructions.
(e) Balance limits—(1) Retainer and investor depositaries. A retainer or investor depositary must establish an initial balance limit for its TIP main account balance by providing notice to that effect in writing to the TSC. The balance limit is the amount of funds for which a retainer or investor depositary is willing to provide collateral in accordance with § 203.21(c)(1). The depositary must follow the procedural instructions before reducing the established balance limit unless the reduction results from a collateral revaluation as determined by the FRB. That portion of any PATAX or EFTPS tax payment which, when posted at the FRB, would cause the TIP main account balance to exceed the balance limit specified by the depositary, will be withdrawn by the FRB that day.
(2) Direct investments. An investor depositary that participates in direct investments must set a balance limit for direct investment purposes which is higher than the peak balance normally generated by the depositary's PATAX and EFTPS tax payment inflow. The depositary must follow the procedural instructions before reducing the established balance limit.
(3) SDIs. SDIs are credited to the SDI account balance and are not considered in setting the amount of the TIP main account balance limit or in determining the amounts to be withdrawn where a depositary exceeds its TIP main account balance limit.
(f) TIO. Treasury may, from time to time, invest excess operating funds in obligations of depositaries awarded funds under TIO. Such obligations will be in the form of interest-bearing notes payable upon a predetermined period of time not to exceed 90 days. Such notes will bear interest at a rate prescribed by the Secretary by auction or otherwise taking into consideration prevailing market interest rates.