Cal. Pub. Util. Code § 98290

(a) A retail transactions and use tax ordinance may be adopted by the board in accordance with the provisions of Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code, provided that two-thirds of the electors voting on the measure vote to authorize its enactment at a special election called for that purpose by the board.
(b) Notwithstanding Section 7251.1 of the Revenue and Taxation Code, a transactions and use tax rate imposed pursuant to subdivision (a) on or before January 1, 2020, shall not be considered for purposes of the combined rate limit established by that section.
(c)
1. (1) In addition to any other taxes imposed pursuant to this section, the board may impose a retail transactions and use tax pursuant to subdivision (a) after January 1, 2024, if both of the following conditions are met:
  1. (A) The board adopts the ordinance approving the tax before January 1, 2035.
  2. (B) The total tax rate under this subdivision is set at a rate of no more than 0.5 percent.
2. (2) Notwithstanding Section 7251.1 of the Revenue and Taxation Code, a transactions and use tax rate imposed pursuant to this subdivision shall not be considered for purposes of the combined rate limit established by that section.