Invoking a rarely used WTO authority, the US on Wednesday asked China to prove it was trying to contain "rampant" piracy and counterfeiting of American goods from movies to software to drugs, according to media reports. US Trade Representative Rob Portman, saying in a Wall Street Journal interview that he wants "to put the Chinese on notice that we're serious", asked the Chinese to produce evidence of its piracy crackdown including descriptions of cases it has pursued. American movie, software and other copyright industries estimate annual losses of more than US$2.5 billion in China due to counterfeiting.