Cal. Pub. Util. Code § 130409

An amended expenditure plan adopted pursuant to Section 130407 may include a provision to reduce a tax rate to percentages lower than that approved by the voters and may further provide for an increase of the tax rate if it has previously been lowered; but the tax rate may not be increased to a rate above the tax rate approved by the voters. Any revised tax rate may be adopted only if the commission determines, by a two-thirds vote, that the proceeds of the taxes with the altered tax rate will be sufficient to provide for the payment of principal and interest of any limited tax bonds and any other indebtedness incurred by the commission which was to be payable from the proceeds of the retail transactions and use tax.