Despite restrictions on non-Olympic sponsors at the London Games, organisers are facing a challenge from a company that has handed out headphones to members of Team GB.
Diver Tom Daley has been pictured wearing the headphones, and swimmer Laura Robson and footballer Jack Butland have also tweeted about receiving their pairs.
The headphones are made by Beats, co-founded by US rapper and music producer Dr Dre, which is not an official sponsor of the Games. The ones pictured above are worn by hip hop artist Lil' Wayne.
The version give to members of Team GB has been specially designed for the Olympics in the red, white and blue of the union flag.
Robson and Butland's tweets appear to have been removed, but earlier the Team GB goalkeeper used his Twitter account to say: "Love my GB Beats by Dre." Butland also said a Beats representative had visited the team hotel.
The International Olympic Committee (IOC) and the London Organising Committee of the Olympic and Paralympic Games (Locog) have drawn up rules to ensure that official sponsors are protected. Athletes are not allowed to promote brands on websites or through social media.
Channel 4 News called Locog for a comment, but has yet to receive a response.
British Olympic Association (BOA) chef de mission Andy Hunt said he would investigate. The BOA's director of communications, Darryl Seibel, joked: "We had to explain to Andy who Dr Dre was first. That took more time than you might have imagined..."
American athletes are protesting about the IOC rules. They are being led by 400m runner Sanya Richards-Ross, who argues that amateur members of the squad do not receive the level of funding that allows them to concentrate on their sport full time.