Cal. RTC § 19041.5

(a) Notwithstanding any other provision of this part, Part 10 (commencing with Section 17001), or Part 11 (commencing with Section 23001), the provisions of Section 6603 of the Internal Revenue Code, relating to deposits made to suspend the running of interest on potential underpayments, shall apply, except as otherwise provided. A deposit shall not be considered a payment of tax for purposes of filing a claim for refund pursuant to Section 19306, converting an administrative action to an action on a claim pursuant to Section 19335, or filing an action pursuant to Section 19384, until either of the following occurs:

(1) The taxpayer provides a written statement to the Franchise Tax Board specifying that the deposit shall be a payment of tax for purposes of Section 19306, 19335, or 19384.

(2) The deposit is used to pay a final tax liability.

(b) Section 6603(d) of the Internal Revenue Code is modified to substitute the phrase “notice of proposed deficiency assessment under Article 3 of Chapter 4 of this part” for “30-day letter” in each place that the phrase “30-day letter” appears.

(c) In the case of any amount held by the Franchise Tax Board as a deposit in the nature of a cash bond pursuant to the provisions of this section prior to the amendments made by the act adding this subdivision, the date that the taxpayer identifies that amount as a deposit made pursuant to this section, as amended by the act adding this subdivision, shall be treated as the date that the amount is deposited for purposes of this section, as amended by the act adding this subdivision.