Among the privileges enjoyed by the Hohenzollern Royal House of Romania was a postal, telegraphic and telephonic tax exempt for almost the entire period they ruled Romania's destiny: 10th of May 1866 - 29th of December 1947.
Other of Romania's state authorities, but only up to The 1st of January 1930 enjoyed similar privileges.

      1. 1. Regulations regarding correspondence postal tax exempt
      Circular postal order NR. 274.658/21st December 1929 (1, nr.1/1930) established the suppression of all postal gratuities enjoyed by state, county and city authorities, starting the 1st of January 1930. Even the letter correspondence of       His Majesty the King, Royal House and Regency were to be franchised by a special mark.
      Will all these, at least since the 1st of April 1933 Royal house correspondence enjoyed a postal stamp exempt.
      The Law for the Royal Cultural Foundations, dated Bucharest, the 14th of April 1933, stipulated the following (2, NR. 88/14th of April 1933):
      Art. 1. Carol I Royal University Foundation, Prince Carol Foundation, Bucharest, Ferdinand Foundation, Iasi, and the Experimental Research Institute King Carol II from Cluj will form a union named the Royal Cultural Foundations of Romania.
      Art. 2. Besides the cultural Foundations named at art. 1. Will be established in Bucharest, according to a special statute, and will join the union, the King Carol II Literature and Art Foundation, with the goal of helping by all means the development of a higher culture in Romania…
      Art. 11. The Royal Cultural Foundations and Establishments set up for the fulfillment of their role are juridical persons. They are registration and fiscal tax exempted, postal tax exempted, as well as any other state, county or city tax exempted…
       Almost two years later, circular postal order NR. 240.620, dated 31st of January 1935 (1, Nr./1935, page 80) stated that:
      …regarding the decision of the P.T.T. direction dated 16th of January 1935, the Royal Cultural Foundations, as well as the Cultural homes pendants, are entitled to forward, tax exempt, only letter and message correspondence. Regarding magazines and various publications edited by the Foundations and Cultural Homes, as well as postal orders, invitations to balls, citations, etc. they will be forwarded taxed according to P.T.T. tariffs.
      This order was amended by another circular order, Nr.34.190/th.of February 1935, by which it was established that:
      Royal Cultural foundations and Cultural Homes pendants, are entitled to forward, tax exempt, magazines and different publications edited by the above mentioned institutes.
      For the Prince Mircea Society from Cluj, there are no known documents, for the moment, that foresee a postal tax exempt for its postal correspondence, but, probably, these documents exist.
      Although this society did not have the title "Royal", it was included in this study, as having the name of a person belonging to the Royal House.
The Law for postal, telegraphic and telephonic exploitation from 1938 (2, Nr. 143/25th of June 1938) established the following gratuities for the Royal house and the Royal Cultural Foundations:
      …Art. 77. There are tax exempted the following:
      a) Postal expenditures of all kinds, telegraphic and telephonic correspondence of His Majesty The King and His Majesty the High Prince of Alba Iulia, of all members of the Royal and Princely family
      b) Postal expenditures of all kinds and telegraphic correspondence regarding work attributions
by the Royal and Princely House Administration, the Royal Crown Domain administration, the Royal cultural foundations, authorities and private….
       The postal tax exempt for the Royal house and its Cultural Foundations existed until the 30th of December 1947, when king Mihai abdicated. .
      2.The marking of correspondence that is tax exempted.
        The correspondence of King Carol the second and his family was sent in envelopes having in the upper corner the title CASA M.S. REGELUI (His Majesty's House), underlined with two thin parallel lines, or other similar titles
The correspondence of the Royal Cultural Foundations were sent in envelopes printed in the left upper corner with the name of the foundation, the address and the monogram of King Carol II CC in the case of King Carol II Foundations, or a crown in the case of Ferdinand I Foundation.
      A part of these envelopes were printed with a rectangle, in the right upper side, with the inscription "Recunoscuta ca / persoana morala / si juridica. Scutita / de plata taxelor / de timbru si inre- / gistrare si taxele / postale prin legea / publicata in Mo-/ nitorul Oficial / Nr. 88/933" (Known as moral and juridical person. Exempted of postal, fiscal and registration taxes by law 88/933, published in the official Bulletin)
     On other envelopes the rectangle was replaced by a rectangular stamp in blue ink (93 x 35 mm):
"Fundatiunea Regelui Ferdinand I / Scutita / de taxele de timbru si inregistrare, de / taxele postale, precum si de orice impo- / zite catre stat, judet sau comuna. Legea / pentru Fundatiune Culturale Regale pub- / licata in Monitorul Oficial, partea I No 88 / din 14 aprilie 1933" (King Ferdinand I Foundation, fiscal, registration and postal tax exempted, as well as any tax to the state, county or city. The Law for the Royal Cultural Foundations Nr. 88/14th of April 1938 published in the Official Bulletin).
      Correspondence for Prince Mircea Society was sent in envelopes printed with its full name in the left upper corner. In the right upper corner there was a violet stamp with three lines: "Scutit de timbru conf. Ord. No. / 147144 al Ministerului de Finante / din 7 iunie 1927" (Fiscal Tax Exempt acc. to order Nr. / 147144 of Ministry of Finance/ from the 7th of June 1927). This text explains of a fiscal and not a postal tax exempt.
On the back of envelopes sent by Royal Cultural Foundations there were always attached seals-stamps in different colors (blue, red, violet, green…) with the name of the department from the forwarding institution.
It has not been exactly established why an Aviation Fund stamp was attached near the rectangle with the tax-exempt inscription on such a correspondence sent from Bucharest in February 1939.
      3.Correspondence with Royal insignia marked with postal stamps.
      Between 1933-1947, as well as in the period before 1930 one can find mail with the Royal insignia but stamped with postal stamps. The causes for the marking are multiple and each correspondence has its own explanation.
One must take into account that at the Royal palaces in Bucharest, Sinaia, Balcic, correspondence was sent by persons other than the Royal family, using, many times, official Royal family envelopes.
Also, the Royal Domains Administration sent its mail in personal interest, but used official envelopes, although not tax-exempt.
It is also known of Royal House correspondence marked by postage stamps, but for a philatelic reason.
Postal regulations very clearly stated postal tax-exempt for Royal House as well as Royal Cultural Foundations correspondence for the periods: 1866-1929, 1933-1947.

      Bibliography:
      1.P.T.T. Bulletin, Bucharest, 1930 - 1947;
      2. Romania Official Bulletin, Bucharest, 1930 - 1947.