Chinese audience have long been familiar with TV commercials featuring the country's sports stars such as basketball player Yao Ming or hurdler Liu Xiang.
But during ongoing Beijing 2008 Olympic Games (August 8-24), they are not appearing as frequently as before. Yao's ad slots for China Unicom and PepsiCo and Liu's for Nike and Amway are forbidden from being shown on TV.
According to the Beijing Organizing Committee for the Games of the XXIX Olympiad (BOCOG), from August 1 to 27, advertisements not authorized by the committee featuring athletes or coaches related to the Olympics are banned.
That could be a big blow to advertisers who have been banking on the Olympics to boost their brands and promote their products.
The ban is part of a range of measures introduced by the committee on June 3 to crack down on ambush marketing during the Games.
From July 11 to September 17, all prominent advertising sites in Beijing - including those at the airport, railway stations, main streets and areas around Olympic venues - will be closely monitored and priority will be given to official Olympic sponsors.
Using unauthorized five-ring logos, selling unauthorized versions of the fuwa mascots and trying to persuade the public a company is part of the Olympic family through advertising is subject to the crackdown.
Any violator with illegal advertising or using Olympic symbols without authorization will be punished.
Ambush advertising practices by individuals are also banned. (The term ambush or "guerrilla" marketing was coined by former American Express boss Jerry Walsh, referring to companies that are not official sponsors but hope to gain a halo effect from the Games.)
For example, if a row of spectators is found to be wearing the same logo on their clothes at a Beijing Olympic venue, they will be asked to conceal the brand names.
Similarly, people will not be allowed to take drinks into venues and they are allowed to buy only Coca-Cola or Coke products, the global partner of the International Olympic Committee (IOC) within the venues.
"While promoting a company's products or services, advertising agencies should not make people think the company has any contact with the Olympics if it is not a sponsor," the BOCOG's marketing department deputy director Chen Feng says.