Wal-Mart has had to close temporarily some of its Chinese stores after being accused of selling mislabelled pork.
The local government in Chongqing says the firm falsely advertised the meat as being organic.
China's official Xinhua news agency said officials claimed a total of 63,547 kilogrammes of pork were involved, over two years.
Wal-Mart told the BBC a total of 13 stores have been closed for a 15-day period.
The US firm said some of its employees have been detained by the Chongqing Public Security Bureau.
The retailer said it had sent a task force to co-operate with the investigation and is "taking the necessary steps to ensure this does not recur".
Appetite for safety
Customers may have been attracted to buy "organic" pork following a series of food scandals, some observers suggest.
Earlier in the year, China Central Television reported that one of the country's largest meat processors had bought pigs fed with the illegal additive clenbuterol.
The drug helps produce leaner meat but can be dangerous to people with heart conditions.
The Shuanghui Group had to recall some of its products and apologised to shoppers.
Dozens of people were also reported to have become sick after a separate tainted pork incident in 2009, thought to involve the same substance.
Focus on China
China is one of Wal-Mart's fastest growing markets.
In August, the firm's international chief, Doug McMillon, said it had 344 stores in the country. Of these, 53 had been opened over the previous 12 months.
Net sales were 9.7% up on a year earlier, however a rise in costs meant it reported a loss on its operations.
The pork accusations are not the first time the retailer has been accused of breaking local laws.
In February, China's National Development and Reform Commission accused Wal-Mart, and its French rival Carrefour, of manipulating prices at 19 stores.
Customers had complained the companies had overcharged them on promotional items.
The firms were ordered to pay a combined fine of 9.5m yuan ($1.5m; £955,000) to resolve the matter.
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