The arrest of Yu Yingzeng and her husband Peter Humphrey last year coincid-ed with a Chinese investigation into accusations that the British pharmaceutical company GSK paid bribes to doctors and officials to use its medications.
GSK said it hired Ms Yu and Mr Humphrey last year to investigate a security breach involving a top manager.
Several top executives at the company received anony-mous emails about the bribery allegations as well as a secretly recorded video of the firm's general manager in China, Mark Reilly, having sex with his girlfriend. The company suspected a former employee was behind the emails.
US Embassy spokesman Nolan Barkhouse expressed concern that diplomats would be barred from the August trial.