Union, may be transmitted, in both directions, in closed mails, if that mode of transmission is agreed to by the Offices of origin and destination of the mails, with the assent of the intermediary Office.
Article 18
The high contracting parties engage to adopt, or to propose to their respective legislatures, the necessary measures for punishing the fraudulent use, for the prepayment of postal articles, of counterfeit postage-stamps, or postage-stamps which have already been used. They likewise engage to adopt, or to propose to their respective legislatures, the necessary measures for prohibiting and suppressing the fraudulent manufacture, sale, offering for sale, or distribution of embossed and adhesive stamps in use in the postal service, counterfeited or imitated in such a manner as to be mistakable for the embossed and adhesive stamps issued by the Administration of any one of the contracting countries.
Article 19
The services concerning letters and boxes with declared value, and those of money-orders, postal parcels, collection of bills and drafts, books of identity, subscriptions to newspapers, etc., form the subject of special arrangements between the various countries or groups of countries of the Union.
Article 20
1.—The Postal Administrations of the various countries composing the Union are competent to establish by mutual agreement, in Regulations of execution, all the measures of order and detail which are judged necessary.
2.—The several Administrations may, moreover, make among themselves the necessary arrangements on the subject of questions which do not concern the Union generally, provided that those arrangements are not contrary to the present Convention.
3.—The Administrations interested are, however, permitted to conclude mutual agreements for the adoption of lower rates of postage within a radius of 30 kilometers.
Article 21
1.—The present Convention involves no alteration in the legislation of any country as regards anything which is not provided for by the stipulations contained in this Convention.
2.—It does not restrict the right of the contracting parties to maintain and to conclude treaties, as well as to maintain and establish more restricted Unions, with a view to the reduction of postage rates or any other improvement of the postal relations.
