Chinese authorities have detained five local staffers at the due diligence firm Mintz Group and shuttered its Beijing office.
It is unclear why the US company was raided, but it said it has not received any official legal notice.
The move comes as Beijing prepares to host an annual investor conference this weekend, involving top CEOs such as Apple's Tim Cook and HSBC's Noel Quinn.
Chinese authorities have yet to comment on the incident.
At a regular press briefing, Chinese foreign ministry spokeswoman Mao Ning said she was not aware of the case.