California Code, Corporations Code - CORP § 904

(a) Except as provided in subdivision (b), if any amendment of the articles would make shares assessable or would authorize remedy by action for the collection of an assessment on fully paid shares, it shall be approved by all of the outstanding shares affected regardless of limitations or restrictions on the voting rights thereof.

(b) If a corporation is a mutual water company within the meaning of Section 2705 of the Public Utilities Code, an amendment of the articles to make the shares assessable or to amend prior article provisions authorizing assessment of shares shall be approved by the holders of at least two-thirds of the outstanding shares of any class affected by the amendment regardless of limitations or restrictions on the voting rights thereof.  However, if the amendment would authorize remedy by action for the collection of an assessment on fully paid shares, the amendment shall be approved pursuant to subdivision (a).