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".

Exceptions can only be permitted by the IOC Executive Board.

The rule helps to protect lucrative IOC and Olympic Games sponsorship deals and prevent "ambush marketing" by companies not paying to be associated with the event.

It has long been challenged by athletes, however, who face penalties if they thank or praise other sponsors without permission.

It normally comes into operation nine days before the Opening Ceremony of the Olympic Games and continues for three days after it.

If the German courts do ultimately rule it unlawful, it could potentially lead to a domino effect wherein similar decisions are made across Europe.

"If these guidelines are too restrictive in their detail, the athletes and their potential sponsors could be abused and the marketing of the individual restricted," Germany's national competition regulator told Sport-Informations-Dienst in a statement.

A date for a court case has not yet been set, meaning this is considered unlikely to happen until after next year's Winter Olympic Games in Pyeongchang.

The DOSB is responsible for implementing these rules in Germany on behalf of the IOC.

Under an amendment of Rule 40 passed by the IOC in 2015, non-sponsors who have an ongoing contract with an Olympic athlete are permitted to apply to the relevant National Olympic Committee for a waiver to use an athlete in their advertising.

This must form part of a campaign, however, that had started at least four months before the Olympics and run continuously.

The IOC have vowed to "cooperate in coordination with the DOSB" on the specific case.

IOC guidelines on the implementation of Rule 40 at Pyeongchang 2018 can be read here