The department may in any resolution of issuance define the events of default including among others default in the payment of the principal or interest upon or premium due upon any debentures or default by the department in the observance of any of the covenants, agreements or conditions on its part to be performed under the resolution of issuance and may provide that upon the happening of any such event of default the holders of not less than the majority in aggregate principal amount of the debentures at the time outstanding will be entitled to declare the principal of all of the debentures then outstanding and the interest accrued thereon to be immediately due and payable.