Coke and Pepsi are at odds over the rights to use the image of a well known Chinese basketball player, Yao Ming, for promotional purposes.

The Houston Rockets star's image is being used on bottles of Coke in Shanghai as part of a promotion only months after he signed a major sponsorship deal with Pepsi.

Yao has demanded that Coke withdraw the products bearing his image. However, Coca-Cola said it is entitled to use the image under the terms of a three-year sponsorship deal it has with the Chinese national team of which Yao is a member. Under that deal, Coca-Cola is allowed to feature the image of up to three members of the team.

The dispute is similar to the furore which blew up between the two major brands over the use of the image of David Beckham last year during the soccer World Cup. Once again, this boiled down to a conflict between two perfectly legal contracts, one with an individual and one with a federation.

Both cases have underlined the pitfalls involved when brands sign up individual sportsmen or women who also may be subject to other contracts with their respective federations, clubs or national teams. Some have suggested that this is ambush marketing by Coca-Cola but it could equally be said that PepsiCo and Yao's advisers must have been aware of the existing contract and could have foreseen the conflict.