Cal. Rev. & Tax. Code § 5152

In an action in which the recovery of taxes is allowed by the court, if the court finds that the void assessment or void portion of the assessment was made in violation of a specific provision of the Constitution of the State of California, of this division, or of a rule or regulation of the board, and the assessor should have followed the procedures set forth in Section 538 in lieu of making the assessment, the plaintiff shall be entitled to reasonable attorney’s fees as costs in addition to the other allowable costs. This section is ancillary only, and shall not be construed to create a new cause of action nor to be in lieu of any other provision of law.