Section 603 of the California Corporations Code provides generally for shareholder action by written consent, unless otherwise prohibited in the articles of incorporation.  Subdivision (c) of that statute provides that a consent may be revoked personally or by proxy by a writing received by the corporation before written consents constituting sufficient to take action have been filed with the corporation's secretary, but not thereafter.  

The Nonprofit Corporation Law marches to the beat of a different drummer.  Sections 5513, 7513 and 9413 each allows members to take action without a meeting by written ballot (unless prohibited by the articles or bylaws).  Subdivision (d) of each of these statutes provides that a written ballot may not be revoked.  Section 5513, 7513 and 9413 apply to public benefit corporations, mutual benefit corporations, and religious corporations, respectively.  In the case of public benefit and mutual benefit corporations the statutes include the proviso "unless otherwise provided in the articles or bylaws".  This proviso does not appear in the analogous provision of the Religious Corporation Law.  As a result, the default rule under all three statutes is that ballots may not be revoked, but that default rule can be altered by the articles or bylaws of a public benefit or mutual benefit corporation.