"Boston Fee Party"

From early 1980s until the early 1990s, American Express was known for cutting its merchant fees (also known as a "discount rate") to merchants and restaurants if they accepted only American Express and no other credit or charge cards. This prompted competitors such as Visa and MasterCard to cry foul for a while as the tactics "locked" restaurants into American Express.
However, in 1991, several restaurants in Boston started accepting and encouraging the use of Visa and MasterCard because of their far lower fees as compared to American Express' fees at the time (which were about 4% for each transaction versus around 1.2% at the time for Visa and MasterCard). A few even stopped accepting American Express credit and charge cards. The revolt, known as the "Boston Fee Party" in reference to the Boston Tea Party, quickly spread nationwide to over 250 restaurants across the United States, including restaurants in other cities such as New York City, Chicago, and Los Angeles. In response, American Express decided to reduce its discount rate gradually to compete more effectively and add new merchants to its network such as supermarkets and drugstores. Many elements of the exclusive acceptance program were also phased out so American Express could effectively encourage businesses to add American Express cards to their existing list of payment options.
Currently, American Express' average US merchant rate is about 2.5%, while the average Visa and MasterCard U.S. merchant rate is about 2% (Visa/MasterCard signature debit cards are at 1.7%). Some merchant sectors, such as quick-service restaurants including McDonald's, have special reduced rates to accommodate business needs and profit margins.
Costco still has an exclusivity agreement with American Express; however, Costco's agreement with Amex was the result of a long negotiation process for exclusive acceptance with multiple parties that also included Visa, MasterCard, and Discover.