(a) A credit union shall not impose any charge on a member or depositor holding a periodic certificate for funds for the failure of such member or depositor to invest, or for the late investment of, any agreed periodic installment investment in such a periodic certificate for funds. A credit union shall pay interest on periodic certificates for funds at the same rate of interest per annum as is paid on certificates for funds as to which a member or depositor has not agreed to make periodic installment investments.
(b) As used in this section “periodic certificate for funds” means a certificate for funds under which a member or depositor undertakes to make periodic investments of a specified amount into one account, except, however, a periodic certificate for funds shall not mean an impound account established for the purpose of payment of taxes or other expenses and obligations in connection with a loan secured by real property.