China’s anti-monopoly regulator announced Monday that it was investigating potential violations of antitrust law by Nvidia, the U.S. company that makes a vast majority of the computer chips that power artificial intelligence systems.

The inquiry, a rare move by Beijing, comes a week after the Biden administration expanded curbs on the sale of advanced U.S. technology to China. In the days since, the Chinese government announced that it would ban the export of several rare minerals to the United States and imposed sanctions on more than a dozen U.S. defense firms and defense industry executives.

Together, the moves by Beijing signal its willingness to engage in supply chain warfare as the policy contest over trade and the control of technology escalates between the world’s two largest economies.

The battle has made AI chips into one of the world’s most sought-after technologies, and Nvidia has cornered the market, accounting for 90% of global sales by the end of last year. Nvidia’s dominance helped it become one of the most valuable companies in the world over the past year.

Graham Webster, an academic focused on geopolitics and technology at Stanford University, said China had a variety of tools it could use to go after foreign companies and show its opposition to U.S. policy. “Nvidia is a pretty obvious target,” he added.

China’s State Administration for Market Regulation said Monday that it was investigating Nvidia for violating commitments made during its acquisition of Mellanox Technologies, a company that makes computer networking equipment. The Chinese regulator approved Nvidia’s acquisition of the company in 2020 with conditions to prevent anti-competitive practices and ensure supplies to China.

Nvidia said in a statement that it was “happy to answer” questions from China’s regulators. “We work hard to provide the best products we can in every region and honor our commitments everywhere we do business,” the statement said.

As the Biden administration has progressively tightened restrictions on Nvidia’s chip sales to China, the company has responded by offering less powerful versions of its chips to the Chinese market.

Officials in Washington, in trying to prevent Chinese companies from buying advanced chips and the machines to make them, say that the technology is essential not just for smartphones and chatbots but also for military superiority.

Chinese tech companies have resorted to stockpiling the chips, while also turning to smugglers and front companies to secure supplies. At the same time, Beijing is pouring large sums of money into its own chip companies in an attempt to make its tech sector less reliant on foreign technology.

“Well before the Biden administration, the Chinese government wanted greater self-reliance on key technologies,” said Webster, a scholar at the program on geopolitics, technology and governance at Stanford.

The Biden administration has been considering further restrictions on global sales of AI chips that could affect Nvidia and its competitors. One new rule could impose more requirements on companies from the United States and other countries when shipping advanced AI chips to China, to try to ensure they are not breaking existing U.S. rules, according to two people familiar with the plans who were not authorized to speak publicly.

The new rule would build on letters that the U.S. government sent to Samsung and Taiwan Semiconductor Manufacturing Co., two of the world’s largest chip companies, ordering them to stop sending advanced chips to China. The Biden administration had discovered that TSMC made some components for AI chips produced by Huawei, the Chinese telecommunications company, in violation of export controls.

Another pending rule from Washington could impose licensing requirements and caps on the number of chips that could be sold in certain countries, as well as security standards for those buying larger clusters of AI chips.

Alan Estevez, a U.S. Department of Commerce official who oversees export controls, declined to comment on the pending rules, but said that the department was continuing to investigate how TSMC chips could end up in Huawei’s AI products.

The Chinese government’s antitrust investigation of Nvidia is not the first time Beijing has targeted U.S. chipmakers.

In October, a think tank with ties to China’s internet regulatory agency called for a review of Intel, the American tech company, for selling products that “constantly harmed” China’s national security and interests. The last company subject to a cybersecurity review was the American chipmaker Micron, which was ultimately cut off from supplying chips to a significant portion of the Chinese market. Another American chipmaker, Qualcomm, paid a $975 million fine in 2015 after the Chinese government investigated it for anti-monopoly violations.