The group says that it no longer has any confidence in the chairman of the International Federation (UIPM) Klaus Schormann and demands that the entire board of UIPM resign.
The activists write in a letter, according to the site Inside the games, that "without asking activists and national federations, the board has undermined 109 years of modern pentathlon".
According to Inside the Games, UIPM is afraid that the sport will lose its place in the Olympics after the scandal in Tokyo this summer when a German trainer hit a horse that refused in front of an obstacle.
UIPM has not decided which sport will replace the riding moment.
Modern pentathlon has been on the Olympic program since 1912 in Stockholm and includes the parts fencing, swimming, horse jumping, shooting and running.