Shanghai Food and Drug Administration is testing meat products of a local company which supplies a chain restaurant in central China's Hunan Province after at least one of its beef steaks were found to contain duck meat.
Shanghai Pinshang Food Co, based in Songjiang District, supplies about 200,000 steaks a year to Jono, a popular restaurant chain in Hunan Province.
The Hunan restaurant chain has been ordered to stop selling steak dishes.
All Juno steaks have now been sealed and samples are being tested by Hunan authorities.
Jono blamed its Shanghai supplier for the substandard products.
But Pinshang insists that all their steaks are clean and they have invited the local food watchdog to seal off the factory before a thorough test has a result.
Pinshang says its steaks sold to Jono were all imported and were carefully individually wrapped.
Pinshang was registered in 2010 in Shanghai with total capital of 50 million yuan ($7.37 million).