The global retailer Wal-Mart says it has re-opened 13 stores in the Chinese mega-city of Chongqing after a 15-day shutdown ordered by authorities in a meat packaging scandal.

Wal-Mart said Tuesday it has retrained its staff to comply with local laws and has installed food inspection laboratories at each of its Chongqing stores. It has also set up “afternoon tea sessions” to gather comments from customers.

City authorities closed the stores early this month saying Wal-Mart had sold more than 63,000 kilograms of ordinary pork over two years that was improperly labeled as organic. Several company officials were detained and Wal-Mart was fined more than $400,000.

In its statement Tuesday, the U.S.-based retailer said it is cooperating with the police investigation of those who were arrested and detained. It said it plans to serve its customers with improved products and services.

Last week, the company announced that Ed Chan, Wal-Mart's chief executive in China, was stepping down for personal reasons and that senior vice president Clara Wong was also stepping down.

Local officials told China's official Xinhua news agency this month that they have punished Wal-Mart 21 times since the company entered Chongqing in 2006. They said the company has been sanctioned for exaggerated advertising and for selling expired and substandard food.