China’s Hebei Iron and Steel Group, its biggest steelmaker by output, accused the United States of breaching World Trade Organization rules and said “U.S. protectionism” is damaging the world steel trade, in a statement posted on its website on Thursday.

The U.S. International Trade Commission, a week ago launched a probe into Chinese steel mills accused by United States Steel Corp. of stealing the production setup and recipe for a strong-selling automotive steel alloy and also conspiracy to fix prices.

“The protectionist behavior taken by the U.S. based on purely groundless accusations by U.S. Steel has seriously broken the WTO rules, distorted the normal world steel trade and damaged the essential interests of Chinese steel mills and U.S. steel users,” the statement said.

A previous Chinese hack of U.S. Steel and other companies resulted in indictments of Chinese military personnel in 2014. Then-Attorney General Eric Holder said, at the time, “This is a case alleging economic espionage by members of the Chinese military and represents the first ever charges against a state actor for this type of hacking. The range of trade secrets and other sensitive business information stolen in this case is significant and demands an aggressive response. Success in the global market place should be based solely on a company’s ability to innovate and compete, not on a sponsor government’s ability to spy and steal business secrets. This Administration will not tolerate actions by any nation that seeks to illegally sabotage American companies and undermine the integrity of fair competition in the operation of the free market.”