4.Such unions shall be cooperatives which shall operate in accordance with the following rules:
(a) the number of members shall not be limited;
(b) a member shall have one vote only, whatever the number of shares that he holds, and he cannot vote by proxy;
(c) interest on shares shall be limited;
(d) the annual operating surplus shall be paid into the general reserve or a reserve contemplated in section 88 or distributed or credited to depositors or borrowers proportionately to the business transacted by each with the union.