China has launched an anti-dumping case of U.S. and Russian imports of grain oriented flat-rolled electrical steel amid a rise in Chinese imports of the metal.

China is questioning whether the steel, used in power transformers, was sold below market value by U.S. and Russian mills, according a statement by the Ministry of Commerce.

The investigation comes on the heels of a complaint filed by seven U.S. steelmakers, including U.S. Steel and Russian-owned Evraz Rocky Mountain Steel Mills and TMK IPSCO, into Chinese imports of stainless steel pipes used in oil production.

Last month, a U.S. trade panel unanimously approved a government probe that could lead to steep U.S. duties on an estimated $2.6 billion of the U.S. imports.

In April, a Chinese newspaper quoted a senior industry official as saying China would retaliate if the U.S. decided to investigate the complaint.