USA Boxing, representing the most successful country in the sport's Olympic history, has left the International Boxing Association (IBA) and will join the breakaway federation World Boxing.
Mike McAtee, chief executive of USA Boxing, wrote in a letter to members on Wednesday that the withdrawal was effective immediately.
"USA Boxing will immediately begin the World Boxing application process and submit the required application on the first day of acceptance, on or about May 1, 2023," he added.
"USA Boxing is committed to work tirelessly with World Boxing, like-minded national federations and worldwide Olympic-style boxing community to earn the privilege to be part of the Olympic Movement now and in the years to come."
Swiss-registered World Boxing was set up this month by countries, including the United States and Britain, concerned about the troubled sport's Olympic future.
The IBA, led by Russian Umar Kremlev and suspended by the International Olympic Committee (IOC) in 2019, has denounced World Boxing as a "rogue" organisation.
IBA files complaint
Formerly known as AIBA, it filed an official complaint to the Boxing Independent Integrity Unit on Wednesday against the individuals and entities involved in the breakaway body.
"Following the announcement of the establishment of the rogue international boxing organisation, the IBA has initiated a series of actions that are designed to provide absolute clarity to all boxing stakeholders regarding the autonomy of the IBA as the global governing body of boxing," the IBA said.
"The IBA strongly condemns the efforts of individuals to damage the significant strides taken by the IBA over the last few years to secure boxers' the best future possible.
"Individuals and entities found guilty by the BIIU will face consequences according to the IBA Constitution, Disciplinary and Ethics Code and other key documents concerned."
McAtee said the board of USA Boxing had approved unanimously a resolution to terminate membership, accusing the IBA of failing to uphold the principles of its constitution and to respect the Olympic charter and movement.
Boxing's place in the Olympics after next year's Paris Games remains uncertain, with the sport not on the initial programme for Los Angeles 2028, pending reforms demanded by the IOC.
USA Boxing is certified by the U.S. Olympic and Paralympic Committee as the national governing body for Olympic-Style boxing in the United States.
The U.S. has won 117 Olympic boxing medals, including 50 golds, since 1904 but boycotted the recent IBA women's world championships in New Delhi.
