Ad industry leaders in the US and Europe have been stunned by the court's verdict that a campaign by Nike rebuffing claims that it uses sweatshop labour is not protected by the right to free speech.
Now they fear that activists all over the world will be encouraged to use the courts in their attempts to stop advertisers defending themselves on contentious issues.
Nike, which is being sued by a Californian anti-globalisation campaigner for making false claims about its treatment of workers in the Far East, had argued that its statements were protected by the First Amendment right to free speech.
The company's critics alleged its campaign was hoodwinking consumers.
In Europe, industry chiefs are worried about the implications of the US judgment, which they believe seriously undermines the long-established principle that the right to free speech applies equally to individuals and to commercial organisations.
Andrew Brown, the Advertising Association's director-general, said: "I've never heard of companies not being able to use advertising to make their case. But that's what the Supreme Court has ruled."