Cal. Const. art. XIII C, § 1
Definitions. As used in this article:
(e) As used in this article, “tax” means any levy, charge, or exaction of any kind imposed by a local government, except the following:
(7) Assessments and property-related fees imposed in accordance with the provisions of Article XIII D.
The local government bears the burden of proving by a preponderance of the evidence that a levy, charge, or other exaction is not a tax, that the amount is no more than necessary to cover the reasonable costs of the governmental activity, and that the manner in which those costs are allocated to a payor bear a fair or reasonable relationship to the payor’s burdens on, or benefits received from, the governmental activity.