"On April 10, 2016, the U.S. Postal Service (USPS) was required to roll back prices on many of its postal products and services, including First-Class 'Forever' stamps. This is the first time in nearly a century that the USPS has dropped the price of First-Class 'Forever' (or equivalent domestic letter) postage. Due to the removal of a temporary surcharge (also called an exigent postal surcharge), the prices for nearly all market-dominant products and services, which are those where the USPS is considered to have a monopoly, such as First-Class Mail or Standard Mail (i.e., advertising mail), have dropped. The prices for competitive products, (e.g., Priority Mail, Parcel Mail, and First-Class Package Service), however, have remained the same. Competitive products and services are those in which USPS must compete with other providers (e.g., Fed Ex and UPS) in the open market."
CRS Insight, IN10475
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html