Modern Dairy, China’s largest raw milk supplier is being investigated following reports it knowingly sold cows at auction that tested positive for Bovine Tuberculosis (bTB).

Dairy Co reports that several cows at one of China Modern Dairy Holdings’ units were said to be infected, but it is not certain if milk from these animals was sold on to manufacturers.

Since the announcement, shares of Modern Dairy have fallen sharply.

Mengniu, China’s second largest dairy processor and one of the largest in the world, has also been affected by the incident. Mengniu owns 28% of Modern Dairy and relies on Modern Dairy to provide more than 70% of the milk supply for its premium brand of milk.

Incidents such as this could add to already heightened consumer concerns in China over food safety. Dairy Co reports that since the melamine scandal in 2008, the Chinese authorities and domestic dairy processors have been trying to improve consumer confidence in domestic dairy products.