A national bank or federal savings association, an out-of-state bank, or a state or federally chartered credit union may, subject to the provisions of this chapter, convert into a state bank upon authorization by and compliance with the laws of the United States, adoption of a plan of conversion by the affirmative vote of at least a majority of its directors and the holders of two-thirds of each class of its shares at a meeting held upon not less than ten days’ notice to all shareholders, and upon approval of the superintendent.