The authorities in China have seized 120,000 counterfeit respiratory masks illegally carrying 3M's trademarks, according to the state news agency.
The fake masks were discovered during an inspection of two shipments of the disposable masks arriving at a Shanghai customs site. Several people have been detained as a result of the investigation.
In a statement, 3M said the masks are of poor standard and would be likely to exacerbate rather than mitigate health risks.
Face masks have become a popular choice for Chinese consumers amid high levels of pollution in rapidly industrialising Chinese cities, as well as concerns about diseases distributed via the respiratory route.
In the last few weeks, large sections of northeast China - including capital Beijing - have been thickly covered by a layer of smog that darkened the sky and at some points exceeded World Health Organisation (WHO) recommended limits by more than 25 times.
Image via CNTV