For over four years, China's Ministry of Commerce kept a law unused. Then on Saturday, May 2, 2026, just two weeks before President Donald Trump was scheduled to visit Beijing, China finally activated it. The law, called Announcement No. 21, tells all Chinese citizens and companies that the latest US sanctions on five Chinese oil refineries will not be recognized or enforced. This is the first time China has ever used this legal tool. The law China used has a long official name, but lawyers call it the Blocking Rules. China created these rules in January 2021 but never put them into practice until now. The US Treasury Department triggered this action on April 24, 2026, when it punished five Chinese refineries for buying Iranian oil. The largest company affected is Hengli Petrochemical, based in Dalian, which processes about 400,000 barrels daily. The other four targets are smaller independent refineries in Shandong province. These are called "teapot" refineries, and they have been buying discounted oil from Iran and Russia. China's response is significant. The government says the US measures break international law. Under the Blocking Rules, China can now restrict companies that follow US sanctions. More importantly, foreign banks and shipping companies that refuse to do business with these Chinese firms can face legal action in Chinese courts. Trump is expected to arrive in Beijing on May 14 and 15 for a summit with President Xi Jinping. This will be his first visit to China as president since 2017. By activating this law just before his arrival, China is sending a clear message about its position on these sanctions.