Cal. Pub. Util. Code § 105115

(a) Upon the affirmative vote of a majority of the directors, which shall include an affirmative vote of at least three directors from each county within the district appointed pursuant to subdivisions (a), (b), (c), (d), (e), and (f) of Section 105020, the board may by resolution submit to the voters of the district a measure proposing a retail transactions and use tax ordinance in accordance with the provisions of Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code.
(b) Notwithstanding any other law, the special taxes authorized in this article may also be imposed by a qualified voter initiative pursuant to Chapter 4 (commencing with Section 9300) of Division 9 of the Elections Code if the qualified voter initiative complies with both of the following requirements:
1. (1) The qualified voter initiative proposes a rate for the retail transactions and use tax that is no less than one-quarter of 1 percent.
2. (2) The qualified voter initiative proposes expenditures for the revenues generated from the retail transactions and use tax that are consistent with the purpose of providing a rail transit system under the jurisdiction of the district.