United States Treaty Series (1968)
“ For every article conveyed by services depending on Administrations foreign to the Union, or by extraordinary services in the Union giving rise to special expenses, a surtax in proportion to these expenses. 3.—In case of insufficient prepayment, articles of correspondence of every kind are liable to a charge equal to double the amount of the deficiency, to be paid by the addressees, which charge however may not exceed that which is levied in the country of destination on correspondence not prepaid, of the same nature, weight and origin. ”
