The disgraced American cyclist, who was stripped of his seven Tour de France titles after being part of a doping scandal, had been entered for the US Masters South Central Zone Swimming Championships, which takes place at the University of Texas in his home town.
The event is hosted by the university's Longhorn Aquatics club, whose director Ann Nellis told Press Association Sport: "Longhorn Aquatics and the Jamail Texas Swimming Center are hosting the US Masters South Central Zone Championships.
"Lance Armstrong, a member of the West Hills Athletic Club, registered to participate in that event and was accepted in accordance with US Masters Swimming policy.
"Today we were notified that Mr Armstrong will not be competing, following a request from the International Swimming Federation (FINA) to the US Masters Swimming organisation that his entry not be accepted."
Although he is banned for life from all competitions that adhere to either the US Anti-Doping Agency (USADA) or World Anti-Doping Agency (WADA) codes, it was thought the low-profile US Masters Swimming event fell outside those restrictions.
However, world governing body FINA today released a statement making clear that the event remains under its jurisdiction and is therefore subject to the ban in place.
FINA said: "Following reports on the media referring the participation of Mr Lance Armstrong in the Masters South Central Zone Swimming Championships in Texas (USA), FINA would like to clarify that: 1. This national competition is under the jurisdiction of the US Masters Swimming; 2. FINA Rule DC 15.1 states: 'Subject to the right to appeal provided in DC 13, the testing, therapeutic use exemptions and hearing results or other final adjudications of any signatory to the code which are consistent with the code and are within the signatory's authority, shall be recognised and respected by FINA and its member federations.(...)'.
"Therefore, FINA wrote a letter to the US Masters Swimming (with copy to US Aquatic Sports and USA Swimming) requesting not to accept the entry of Mr Lance Armstrong in the above mentioned competition."
Armstrong, who came clean on his doping past in a television interview with Oprah Winfrey in January, was due to contest the 1,650-yard freestyle tomorrow night, and was also pencilled in for freestyle races over 500 and 1,000 yards.