A Postal tax stamp refers to a stamp which raises revenue for charity or war related projects. Postal tax stamps are similar to semipostals

Semipostal

A semi-postal stamp or semipostal stamp, also known as a charity stamp, is a postage stamp issued to raise money for a particular purpose and sold at a premium over the postal value...

, except their use is mandatory instead of voluntary. They are used to show payment of a compulsory tax on mailing letters and parcels. The taxes often go to a charitable institution or fund.

The postal tax stamp originated in Spain

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 and Portugal

Portugal

Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

. Many Balkan nations and some Latin America

Latin America

Latin America is a region of the Americas where Romance languages  – particularly Spanish and Portuguese, and variably French – are primarily spoken. Latin America has an area of approximately 21,069,500 km² , almost 3.9% of the Earth's surface or 14.1% of its land surface area...

n nations have been the most prolific issuers of postal tax stamps. There are no postal tax stamps in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.