The open letter, written by the German Olympic Sports Confederation (DOSB) Athletes' Commission chaired by fencer Max Hartung, is written as the country's Federal Cartel Office considers legal action against the DOSB - and indirectly the IOC - over a possible violation of competition law through their controversial Rule 40 restrictions.

The letter also calls for 25 per cent of IOC revenues to go directly to athletes and for 10 per cent to be paid to the World Anti-Doping Agency (WADA).

The IOC reject the criticisms and insist the current system is the best to provide adequate backing for athletes and other bodies that support them.

Rule 40.3 of the Olympic Charter warns that "no competitor, team official or other team personnel who participates in the Olympic Games may allow his person, name, picture or sports performances to be used for advertising purposes during the Olympic Games".

"By submitting to the IOC Charter and thus under Rule 40, it is only marginally possible for athletes worldwide to advertise with partners and sponsors in the economically most important phase of their sporting career," the letter argues. 

"This period is so important for Olympic athletes in particular because they are rather underrepresented in the media presentation in addition to football coverage.

"Athletes are losing crucial advertising revenues and possible further partnerships that can contribute to securing their financial and economic situation. 

"In addition, at the Olympic Games, the placed athletes - in contrast, for example, to World or European Championships - get no bonuses. 

"From our point of view, Rule 40.3 constitutes an impermissible interference with the constitutionally guaranteed freedom of profession under German and European law and thus with the exercise of the profession as an athlete."

The letter continues by claiming that Rule 40 "monopolises the marketing of the Olympic Games, their terms and symbols in conjunction with the participating athletes".

Rule 40 is a major reason why companies are willing to sign up as part of the lucrative The Olympic Programme (TOP) sponsorship scheme which guarantees huge exposure during Games-time. 

The letter continues by arguing how athletes "participate negligibly in the marketing profits of the IOC, even though they provide their far-reaching image and personality rights".

The IOC claim that they redistribute 90 per cent of their revenues back to the sports movement.

A detailed breakdown has not been given, but this percentage includes funds to Organising Committees, National Olympic Committees (NOCs) - especially the United States Olympic Committee - International Federations (IFs) and the Olympic Channel. 

Money directly allocated to athletes via Olympic Solidarity funding was only a small amount of this while WADA's direct budget from the IOC is also a fraction of the $5.7 billion (£4.4 billion/€4.9 billion) generated over the 2012 to 2016 Olympic cycle - although the IOC claim the true amount spent combating doping is higher once amounts from IFs and NOCs are factored in. 

"The German Athletes' Commission is recommending a distribution of 25 per cent of the total profit from the marketing and transmission revenues of the IOC to athletes' interests," the letter adds.

"It must be ensured that the funds go directly to the athletes.

"Against the background of international doping scandals and the visible weaknesses of international anti-doping management, the German Athletes' Commission demands 10 per cent of the profits from marketing and broadcasting rights to finance an independent anti-doping management and thus an independence of the WADA.

"We have concrete proposals for both pillars - athletes and anti-doping management.

"The German Athletes Commission believes that these demands will significantly contribute to a positive development of the socio-economic conditions of all athletes worldwide. 

"In addition, anti-doping management - independent of sports - is of the highest relevance.

"Athletes see it as the only way to restore credibility and value creation to the international, organised sports.

"The athletes expect a maximum of transparency and a complete disclosure of the marketing and transmission income as well as the use of funds by the sports organisations."

The DOSB said in a statement that they are "optimistic" the Federal Cartel Office proceedings will come to a conclusion soon.

"Basically, it is already possible for the athletes to implement promotional activities with their sponsors during the frozen period [where Rule 40 is applied]," they added. 

"Most recently, almost all athletes of the German team submitted and approved corresponding applications for the Olympic Winter Games Pyeongchang 2018. 

"The scope of the possible promotional activities will expand in the future."

They also defended IOC expenditure.

"Almost half of the 90 per cent [redistributed revenue] is related to the organisation of the Olympic Games, the most outstanding event for athletes worldwide. 

"The rest of the distribution will be made to the international sports organisations, so that athletes can have competitions and conditions in which competitive sports are possible. 

"Of course, during the Olympic Games pictures of athletes in the television broadcast are shown - this is in the very interest of the athletes."

The DOSB Commission have an increasingly complex relationship with the DOSB itself.

Hartung and canoeist Silke Kassner, his deputy, announced plans last year to form a breakaway group after criticising a perceived lack of independence while operating under the DOSB umbrella.

They proposed a new organisation funded by private and public contributions, donations and marketing revenue which would have its own office and director at a cost of between €300,000 (£270,000/$350,000) and €400,000 (£360,000/$470,000).

The full letter can be read here.