The group have also called on the UIPM vice-presidents - Spain's Juan Antonio Samaranch, a senior International Olympic Committee (IOC) member, France's Joël Bouzou, Russia's Viacheslav Aminov, Kazakhstan's Berik Imashev and Mexico's Juan Manzo Orañegui - along with general secretary Shiny Fang of China and the remaining Executive Board members to resign.

The UIPM Executive Board officially confirmed yesterday it passed a motion to remove riding from the sport.

A briefing document seen by insidethegames revealed the governing body was concerned for its Olympic future, with the IOC warning it would "only accept a proposal without riding" for the Los Angeles 2028 Olympic programme, which is set to be decided in December.

The decision has led to an impassioned response by current and former pentathletes.

In a letter seen by insidethegames, a group of 667 athletes, including Britain's Tokyo 2020 champions Joe Choong and Kate French, the Czech Republic's London 2012 gold medallist David Svoboda, and Sydney 2000 bronze medallist Kate Allenby of Britain have called for Schormann and the entire Executive Board to resign following a decision they described as having "undermined 109 years of Modern Pentathlon".

"As Modern Pentathletes, past and present, we are shocked at the UIPM Executive Board’s decision to remove the equestrian discipline," the letter read. 

"We unanimously declare a vote of no confidence in the President and complete Executive Board. 

"Baron Pierre De Coubertin created Modern Pentathlon specifically for the Olympic Games to showcase the ultimate athlete.  

"Without consulting its athletes and member federations, the Executive Board has undermined 109 years of Modern Pentathlon.

"The Board say they are responding to pressure from the International Olympic Committee. 

"We are all aware of the challenges Modern Pentathlon faces. 

"We must always look to the future and keep our sport moving forward.

"The actions of the current President and Executive Board show that we need a new Board capable of planning for the sport’s long-term interests, standing up for its athletes and protecting its place in the Olympic Games.

"Therefore, we call upon the UIPM EB and President to resign."

The names of the 667 athletes can be viewed here.

In May, Fang extended her contract as secretary general until 2025.

Schormann is set to be re-elected for an eighth term as UIPM President at Congress in November after running unopposed.

After the end of another four-year term, he will have been UIPM President for 32 years.

In response to the open letter, the UIPM told insidethegames: "UIPM is fully aware of the concerns voiced by current and former athletes relating to the Executive Board decision to replace riding in modern pentathlon.

"All athletes - who were the recipients of an open letter from the EB on November 4 - are invited to participate in an open dialogue on this matter so that they can better understand the background. 

"The open dialogue will be scheduled within the next week.

"All opinions and ideas are welcome and will be fully taken on board for the fifth discipline discussion according to the announced criteria.

"As part of UIPM's normal democratic process, an electoral UIPM Congress will take place in three weeks on November 27-28, where member federations will have the opportunity to discuss and debate all motions on the agenda. 

"All athletes are encouraged to consult and talk to their National Federations about any concerns or proposals.

"UIPM is committed to working with our current and future athletes to help them to realise their dreams in the future Olympic Games."

In a statement yesterday, the UIPM claimed the decision was "necessary to save modern pentathlon in the future".

"We know that this information will be surprising and even shocking to you," it added.

"It is not very long since we made a commitment to review and protect the riding discipline in the wake of the rescheduled Tokyo 2020 Olympic Games.

"But life within the Olympic movement changes fast.

"While our sport is confirmed for Paris 2024 with our exciting new format in place (including riding), Los Angeles 2028 is a different matter and we must be flexible and embrace change once again."

The UIPM claimed it needed to present a solution to the IOC before November 24, prior to the scheduled meeting of the Olympic Programme Commission at the end of the month.

The solution will include a replacement element, which must meet a series of criteria set out by the UIPM, governed by the narrative of de Coubertin in searching for the "most complete athlete".

Cycling has been mooted as a possible replacement for riding. 

The pressure from the IOC comes following a disastrous Tokyo 2020 event in which several horses refused to jump for riders, including Saint-Boy, ridden by Germany’s Annika Schleu, who was leading the competition entering the riding event.

German coach Kim Raisner was later sent home following video footage showing her punching Saint-Boy, while Schleu was criticised for repeatedly whipping the distressed horse.

Schormann described the Tokyo 2020 horse-abuse scandal as a "vital learning moment", while People for the Ethical Treatment of Animals has called for all equestrian disciplines to be removed from the Olympics outright.

Riding will remain on the modern pentathlon programme for Paris 2024, alongside swimming, fencing and laser run, in a new 90-minute long format to increase viewership of the sport and make it more attractive to a younger audience.

It remains to be seen how riding being dropped will impact this new format.