China has ruled that Nvidia violated anti-monopoly laws with a high-profile 2020 deal, ratcheting up the pressure on Washington during sensitive trade negotiations.

The U.S. chipmaker was found in violation of antitrust regulations after the acquisition of networking gear maker Mellanox Technologies, China's State Administration for Market Regulation said after concluding a preliminary investigation. Nvidia’s shares fell about 2% in pre-market trading, while U.S. stock index futures pared gains.

The surprise announcement emerged as U.S. and Chinese officials headed into a second day of wide-ranging negotiations in Madrid over tariffs, which could shape the relationship between the world’s two largest economies. Over the weekend, China also said it was launching an anti-dumping investigation targeting a type of semiconductor made by U.S. companies including Texas Instruments. Its shares fell roughly 2% in pre-market trading.