A group of US athletes protested on Twitter on Sunday over curbs on appearing in commercials during the Olympics in what looked like a concerted challenge to rules designed to protect Games sponsors.
Athletes including Dawn Harper, gold medallist in the 100 metres hurdles in Beijing four years ago, took to the social networking site to call for the restrictions to be relaxed.
"I am honored to be an Olympian but #wedemandchange #rule 40," Harper tweeted, accompanied by a picture of a group of US teammates in a meeting room. Others including triple Olympian Sanya Ross-Richards echoed the message.
The target of their ire was rule 40 of the Olympic Charter which forbids athletes from taking part in advertising for anyone except sponsors during a Games.
The rules protect the 11 international companies including Visa, McDonald's and Coca-Cola which help to bankroll the Olympic movement, paying around $100 million each for four years of global rights to sponsor a winter and summer Games.
Those companies and sponsors of national Olympic committees are exempt from rules designed to prevent what is called "ambush marketing", non-sponsors getting free publicity on the back of the Games.
However, the curbs mean that athletes are cut off from some of their own individual sponsors just when they are enjoying maximum exposure.
Guidance issued to athletes and their agents before the Games warned them that they risk sanctions including disqualification if they broke the rules.
The International Olympic Committee (IOC) has been actively encouraging athletes to use social media during the Games which opened on Friday.
However, the guidelines on blogging contain a warning about adhering to the rules on advertising.