Twenty high-profile British athletes led by the sprinter Adam Gemili have taken the extraordinary step of launching legal action against the British Olympic Association to force it to relax its “unjust and unlawful” sponsorship rules for Team GB stars.

The landmark challenge comes after the BOA refused to follow the lead of the German and US Olympic federations, who have allowed athletes more freedom to market themselves during the Tokyo 2020 Games.

Gemili, who is a BOA athlete representative, said the unprecedented action had come after the athletes were brushed aside by the BOA. He confirmed Katarina Johnson-Thompson, Sir Mo Farah and Laura Muir were among those who had signed a petition supporting the legal action.

“The situation as it stands is completely unfair,” Gemili said. “For most athletes the Olympics is that one chance every four years to be in the limelight – and we want to be able to recognise those sponsors that have helped us make it to the Games.

“The legal advice we have got is that we have a very strong case. Despite attempts to engage the BOA, we’ve had no indication from them that things will get better. We continue to get brushed aside.”

Under the International Olympic Committee’s infamous rule 40, athletes have historically not been allowed to use their image, name or performance for any advert in or around an Olympics. Yet this year the IOC accepted that countries could decide to be more flexible after rule 40 was successfully challenged in German courts.

However, British athletes have been left frustrated after the BOA only slightly softened its stance to allow them to issue a generic thank you message during the Games period “provided it doesn’t contain any Olympic branding, such as a medal or Team GB kit or references”.

That, say the British athletes, adds zero value to potential sponsors. In a letter delivered to the BOA on Friday they asked for eight changes to the current rules, including permitting athletes to use terms like “medal, gold, silver, bronze, winter or summer games” in advertising during Tokyo 2020, along with being able to thank more widely non-Olympic brands who support them.

Another bone of contention among the athletes is that, while the BOA generates tens of millions of pounds from sponsors, many athletes hoping to represent Team GB have to take out jobs. In response the BOA pointed out that it was an entirely independently funded organisation whose main purpose was to take athletes to the Olympic Games and Youth Olympic events.

“Rule 40 is an IOC rule which we apply in our territory and is the protection that allows us to fund such activities for all athletes, regardless of their sport, status or personal sponsors,” a spokesperson said.