If a proposed amendment to a social purpose corporation's articles of incorporation would materially change one or more of the social purposes of the corporation, in addition to approval in accordance with RCW 23B.10.030, the amendment to be adopted must be approved by two-thirds of the voting group comprising all the votes entitled to be cast on the proposed amendment, and by two-thirds of the holders of the outstanding shares of each class or series, voting as separate voting groups, and of each other voting group entitled under the articles of incorporation to vote separately on the proposed amendment. The articles of incorporation may require a greater vote than that provided for in this section.